Category: Class 11 Chemistry Objective Questions

Chemistry Multiple Choice Questions on “Periodic Trends in Properties of Elements”.

1. Atomic radii ____________ along the periods.
a) Increases
b) Decreases
c) Remains constant
d) Irregular
Answer: b
Clarification: Atomic radii decreases along the periods because as the number of electrons increases in the same shell of the atom, the effective nuclear attraction increases, thereby reducing the distance between the outer shell and the nucleus i.e. decreasing atomic radii.

2. O^2-, F^–, Na⁺ and Mg²⁺ are called as __________
a) Isoelectronic species
b) Isoneutral species
c) Isotopes
d) Isobars
Answer: a
Clarification: O^2-, F^–, Na⁺ and Mg²⁺ are known as isoelectronic species as they all have the same no. of electrons(10). Isotopes contain the same no. of protons but a different number of neutrons. Isobars have the same mass number but a different atomic number.

3. X_(g) → X⁺_(g) + e^–. What does this chemical reaction need to occur?
a) Catalyst
b) Electron affinity
c) Electropositivity
d) Ionization energy
Answer: d
Clarification: The minimum amount of energy that is required to remove an electron from an atom is called Ionization enthalpy. It is expressed in the units KJ/mol. Electron affinity is the change in the energy when we add an electron to a neutral atom. Electropositivity is a metallic characteristic. A catalyst speeds up the reaction.

4. What is the correct order of electronegativity among the following options?
a) Lib) Lic) Li>Na>K>Cs>Rb
d) Li>Na>K=Rb>Cs
Answer: d
Clarification: Electronegativity is the measure of the ability to attract shared electrons to itself of an atom in a chemical compound. The values of electronegativities of Li, Na, K, Rb and Cs are 1, 0.9, 0.8, 0.8 and 0.7 respectively.

5. Ionization energies are always positive.
a) True
b) False
Answer: a
Clarification: As the ionization energy is the minimum amount of energy that is required to remove an electron from an atom. As the energy is always needed for the removal of an electron from an atom, the values of ionization energies are always positive.

6. What is the oxidation state of Mn in KMnO₄?
a) 5
b) 6
c) 7
d) 4
Answer: c
Clarification: The total charge of the compound KMnO₄ is zero as it is a neutral and stable compound. As we know the oxidation states of K and O are +1 and -2 respectively. So +1 + Mn charge + 4(-2) = 0; Mn charge = 7.

7. The relationship between Li, Mg and Be, Al is called the __________ relationship.
a) Diagonal
b) Periodic
c) Group
d) Triangle
Answer: a
Clarification: The Elements Li and Mg, Be and Al are similar to each other in the case of formation of different compounds in a similar composition. They have a sort of similar behaviour with each other, so they are said to be in a diagonal relationship as per their place in the periodic table.

8. N₂O is a _________
a) Tear gas
b) Laughing gas
c) Acid
d) Base
Answer: c
Clarification: N₂O is called laughing gas as it has euphoric effects after being inhaled. It is one of the World Health Organization’s Essential Medicines. it is used for recreational and anaesthetic purposes mostly.

9. Which of the following is superoxide?
a) K₂O
b) Na₂O
c) MgO
d) KO₂
Answer: d
Clarification: In the superoxide of the element, the oxygen’s oxidation state is given by -1/2. In peroxides, the oxidation state of oxygen is -1 as in case of hydrogen peroxide. The oxygen’s oxidation state in KO₂ is -1/2.

10. What can be tested using a litmus paper?
a) Acidic nature only
b) Basic nature only
c) Both acidic nature and basic nature
d) Nothing
Answer: c
Clarification: A litmus paper is a dye that is extracted from lichens. It used to test acidic nature and basic nature of a substance. Red colour indicates acidic nature and blue colour indicated basic nature. Neutral litmus paper is purple in colour.

Chemistry Multiple Choice Questions on “Thermodynamics – Enthalpies for Different Types of Reactions”.

1. Enthalpy of combustion as always ________
a) positive
b) negative
c) 0
d) infinity
Answer: b
Clarification: Enthalpy of combustion is the enthalpy change that takes place when one mole of a compound undergoes complete combustion in the presence of oxygen. It is represented by ΔHc, it is always negative because the process of combustion is exothermic.

2. Calculate the heat of combustion of ethane, in the reaction C₂H_6(g) + 3 1/2O_2(g) → 2CO_2(g) + 3H₂O_(l) where the heats of formation of ethane gas, carbon dioxide gas and water liquid are –84.7 kJ mol^-1, -393.5 kJ mol^-1 and –285.8 kJ mol^-1 respectively.
a) -1559.7 kJ mol^-1
b) -155.7 kJ mol^-1
c) -159.7 kJ mol^-1
d) -559.7 kJ mol^-1
Answer: a
Clarification: Given that C₂H₆(g) + 3 1/2 O_2(g) → 2CO_2(g) + 3H₂O_(l) As we know that, ΔHr = Σ ΔH_f[products] – Σ ΔH_f[reactants]; ΔH_c(C₂H₆) = 2 X (-393.5 kJ mol^-1) + 3 X (-285.8 kJ mol^-1) – (- 84.7 kJ mol^-1) – 2 X (0 kJ mol^-1) = ΔH_c(C₂H₆) = – 1559.7 kJ mol^-1.

3. The enthalpy of 435 KJ per Mol is obtained from the conversion of hydrogen molecule into two hydrogen atoms.
a) True
b) False
Answer: a
Clarification: The enthalpy change that occurs when one mole of a molecule breaks into its atoms is known as enthalpy of atomization. The energy released during the conversion of a hydrogen molecule into two hydrogen atoms is enthalpy of atomization.

4. In which of the following reactions the energy released is not an enthalpy of atomization?
a) decomposition of a hydrogen molecule into two hydrogen atoms
b) decomposition of an oxygen molecule into 2 oxygen atoms
c) formation of a water molecule
d) decomposition of chlorine molecule
Answer: c
Clarification: The enthalpy of atomization is an enthalpy change that occurs when one molecule of a molecule breaks into its atoms, but here the of a water molecule formation does not satisfy the definition of the enthalpy of atomization.

5. In case of the decomposition of hydrogen molecule into two hydrogen atoms, the enthalpy of atomization is same as the _________
a) bond dissociation enthalpy
b) enthalpy of formation
c) enthalpy of combustion
d) enthalpy of sublimation
Answer: a
Clarification: In case of the decomposition of hydrogen molecule the enthalpy is the same as enthalpy of atomization as well as bond dissociation enthalpy because the bond association enthalpy refers to the breakage of H-H Bond. So that two hydrogen atoms are formed whereas enthalpy of atomization is the breakage of hydrogen molecules in order to form two atoms.

6. Calculate the carbon carbon double bond energy in ethane from the following reaction, H₂C=CH₂(g) + H₂(g) –> H₃C−CH₃(g) ΔH = −138 kJ/mol. If Bond enthalpies are: C−C = 348; H−H = 436; C−H = 412 in KJ/mol.
a) 498 KJ/mol
b) 593 KJ/mol
c) 508 KJ/mol
d) 598 KJ/mol
Answer: d
Clarification: By following the rule ΔH_r = Σ ΔH_f[products] – ∑ ΔH_f[reactants], we get -(x + 4(412) + 432) + (348 + 6(412)) = -138 KJ/mol; x = 598 KJ/mol. So the carbon carbon double bond energy in Ethane is given as 598 KJ per Mol.

7. Decomposition of sodium chloride into a sodium ion and chloride ion releases energy of 788 KJ per Mol, what is the energy called?
a) lattice energy
b) translation energy
c) dilution energy
d) neutralization energy
Answer: a
Clarification: Lattice enthalpy is the enthalpy change when one molecule of an ionic compound dissociates into its ions and gaseous state. Here sodium chloride is an ionic compound and it decomposes into sodium and chloride ions, so the energy released is lattice energy.

8. Which of the following cycle allows has to analyze reaction energies?
a) carbon cycle
b) born Haber cycle
c) nitrogen cycle
d) chemical cycle
Answer: b
Clarification: An indirect method, in which we can construct an enthalpy diagram is called a Born-Haber cycle as it is nearly impossible to determine lattice enthalpies directly by experiment. It is an approach to analyze reaction energies.

9. Enthalpy of solution can either be positive or ________
a) negative
b) does not exist
c) 0
d) infinity
Answer: a
Clarification: Enthalpy change when 1 mole of a substance is dissolved in a large excess of solvent so that on further delusion no appreciable heat change occurs, is known as enthalpy of solution. It can either be positive or negative depending on the reaction, whether it is exothermic or endothermic.

10. The enthalpy of dilution of a solution is __________ on the original concentration of the solution and the amount of solvent added.
a) dependent
b) independent
c) may be dependent
d) may be independent
Answer: a
Clarification: Enthalpy of dilution is the enthalpy change when 1 mole of a substance is diluted from one concentration to another. So it is dependent on your original concentration of the solution and the amount of solvent added.

Chemistry Interview Questions and Answers on “Redox Reactions in Terms of Electron Transfer Reactions”.

1. What is the oxidation half reaction of Cu⁺² + Zn → Cu + Zn⁺²?
a) Zn → Zn⁺²
b) Cu⁺² → Cu
c) Cu⁺² → Zn⁺²
d) Zn → Cu
Answer: a
Clarification: Oxidation is the loss of electrons by an atom, ion or molecule. It is also known as de-electronation. Here in the above given chemical reaction Cu⁺² + Zn → Cu + Zn⁺², the oxidation half-reaction is Zn → Zn⁺².

2. When a zinc rod is kept in a copper nitrate solution what happens?
a) zinc is deposited on copper
b) copper is deposited on zinc
c) zinc is deposited in the beaker
d) copper is deposited in the beaker
Answer: b
Clarification: When zinc is placed in copper nitrate solution the intensity of the blue colour is produced and copper iron is deposited on zinc. This is a Redox reaction between zinc and an aqueous solution of copper nitrate occurring in a beaker.

3. In this reaction Cu⁺² + Zn → Cu + Zn⁺², what is an oxidising agent?
a) copper
b) zinc
c) hydrogen
d) oxygen
Answer: a
Clarification: Oxidant or oxidizing agent is a chemical substance which can accept one or more electrons and causes oxidation of some other species. Here to accept electrons from zinc, so copper is an oxidizing agent.

4. Loss of electrons is _________________
a) oxidising agent
b) oxidation
c) reducing agent
d) reduction
Answer: b
Clarification: Oxidizing agent is the acceptor of electrons and the reducing agent is a donor of the electrons, where oxidation is termed by loss of electrons by any species and reduction is gain of electrons by any species.

5. Intensity of blue colour increases gradually when _________________
a) copper rod is dipped in silver nitrate solution
b) silver rod is dipped in copper nitrate solution
c) zinc rod is dipped in silver solution
d) copper rod is dipped in zinc rod solution
Answer: a
Clarification: When a copper rod is dipped in silver nitrate solution, a redox reaction occurs between Copper and an aqueous solution of silver nitrate. So the intensity of blue colour increases gradually as silver deposits on the rod.

6. Which of the following is true as per metal activity series?
a) Znb) Znc) Zn>Ag>Cu
d) Zn>Cu>Ag
Answer: d
Clarification: Metal activity series or electrochemical series is a series in the decreasing order of metals which are active during a chemical reaction comparatively with each other. Here, Zinc’s activity is greater than Copper’s activity and Copper’s activity is greater than that of silver.

7. What is a reducing agent of the reaction Cu⁺² + Zn → Cu + Zn⁺²?
a) copper
b) zinc
c) hydrogen
d) oxygen
Answer: b
Clarification: Reductant or reducing agent is a chemical substance which can give one or more electrons and causes reduction of some other species in a chemical reaction. Therefore, zinc is a reducing agent in this reaction.

8. The oxidation number of oxidant increases in a Redox reaction.
a) true
b) false
Answer: b
Clarification: Oxidising agent is also known as an oxidant, the oxidation number of an oxidant decreases in a Redox reaction whereas the oxidation number of reductant increases in a reaction. Reducing agent is known as a reductant.

9. Which of the following is not an oxidising agent?
a) magnesium oxide
b) carbon dioxide
c) ozone
d) sodium hydride
Answer: d
Clarification: Molecules of most electronegative elements, compounds having an element in the highest oxidation state and oxides of metals and nonmetals are examples of oxidising agents. But sodium hydride is a metallic hydride, so it is not an oxidizing agent.

10. Hydrogen peroxide is a ______________
a) oxidising agent
b) reducing agent
c) both reducing and oxidizing agent
d) neither reducing nor an oxidizing agent
Answer: c
Clarification: Hydrogen peroxide, which is chemically written as H₂O₂, is a strong oxidizer as well a reducer. As it contains two hydrogens and to oxygens, it easily looses hydrogen or oxygen i.e. oxidizes and reduces respectively.

Chemistry for Interviews,

Chemistry Multiple Choice Questions on “p-Block Elements – Group 13 Elements: Boron Family”.

1. Are group 13 elements a part of p block elements?
a) Yes
b) No
c) Only a few
d) Only one
Answer: a
Clarification: The last electron enters in the outermost p-orbital in the p block elements, from group 13 to group 18 the entire elements belong to p-block, whereas group 13 is called a boron family. It includes the elements boron, aluminum, gallium, indium and thallium.

2. Which of the following group’s elements have smaller atomic radii?
a) Group 1 elements
b) Group 2 elements
c) Group 13 elements
d) All have the same atomic radii
Answer: c
Clarification: Group 13 elements have smaller atomic radii and ionic radii than those of alkaline earth metals and alkali metals due to the greater effective nuclear charge, atomic radii increases on going down the group with an abnormality at gallium.

3. The atomic radius of gallium is greater than that of aluminum.
a) True
b) False
Answer: b
Clarification: Though the atomic radii increase on going down the group, the radius of gallium decreases unexpectedly because of the presence of electrons in the orbitals which do not screen the attraction of the nucleus effectively. So the atomic radius of gallium is less than that of aluminium.

4. Gallium remains liquid up to __________ Kelvin.
a) 2176
b) 2376
c) 2476
d) 2276
Answer: d
Clarification: Low melting point of gallium is due to the fact that it consists of Ga₂ molecules and gallium remains liquid up to 2276 k. Hence it is used in high-temperature thermometer. Gallium as a chemical symbol that is Ga and its atomic number is given as 31.

5. The ionization enthalpy _________ down the group in the family.
a) Increases
b) Decreases
c) Constant
d) Is a regular
Answer: d
Clarification: On moving down the group, ionization enthalpy decreases from Boron to aluminium, but the next element gallium has slightly higher ionization enthalpy than aluminium due to the poor shielding of intervening d-electrons, it again increases in indium and then decreases in the last element thallium.

6. Inert pair affect __________ down the group.
a) Increases
b) Decreases
c) Constant
d) Is a regular
Answer: a
Clarification: Inert pair effect is the reluctance of the selections of the valence shell to take part in bonding, it occurs due to pore shielding of ns² electrons by intervening d-electrons and f-electrons, down the group, it increases. The below elements of the group exhibit lower oxidation States.

7. Which of the following element exhibits + 3 Oxidation State only?
a) Gallium
b) Thallium
c) Indium
d) Aluminium
Answer: d
Clarification: Boron and aluminium exhibit oxidation state of + 3 only, while gallium, indium and thallium exhibit oxidation states of both +1 and +3. As we move down the group, the tendency to exhibit + 3 Oxidation State decreases this occurs due to the inert pair effect.

8. Which of the following is true regarding reducing character?
a) Gallium < aluminium > indium > thallium
b) Aluminium > gallium > indium > thallium
c) Aluminium > gallium < indium > thallium
d) Gallium > aluminium > indium > thallium
Answer: b
Clarification: Reducing character of the boron family decreases down the group from aluminium to thallium because of the increase in electrode potential value for M³⁺/M, therefore, the correct order is given as aluminium > gallium > indium > thallium.

9. Complex formation is more likely to be possible in __________
a) alkali metals
b) alkaline earth metals
c) boron family
d) equally likely
Answer: c
Clarification: The complex formation in the boron family is greater than the S block elements due to their smaller size and greater charge. So they can form complexes more likely than alkali metals and alkaline earth metals.

10. The compounds formed by the Boron family are __________
a) ionic
b) covalent
c) both ionic and covalent
d) neither ionic nor covalent
Answer: c
Clarification: Ionic compound formation’s tendency increases from Boron to thallium. Boron can only form covalent compounds, whereas aluminium can form both covalent as well as ionic compounds. Gallium forms mainly ionic compounds.

11. What is the chemical formula of aluminium carbide?
a) AlC
b) AlC₃
c) AlC₂
d) AC₃
Answer: b
Clarification: 4 moles of aluminium atom combines with 3 moles of carbon atom on heating, in order to form aluminium carbide. Aluminium carbide is ionic in nature and it also forms methane with water. Its chemical formula is given by AlC₃.

12. When boron reacts with nitrogen which of the following compound is formed?
a) Boron oxide
b) Boron nitrate
c) Boron hydrides
d) Boron nitride
Answer: d
Clarification: On heating, two moles of boron atom combine with one mole of a nitrogen molecule in order to form 2 moles of boron nitride. Aluminium also when reacted with nitrogen forms aluminium nitride in the same way.

13. What forms when boron combines with caustic soda?
a) Formation of oxygen
b) Formation of washing soda
c) Formation of Boron nitride
d) Formation of sodium borate
Answer: d
Clarification: Two moles of boron atoms fuse with 6 moles of sodium hydroxide in order to form 2 moles of sodium borate and three moles of hydrogen molecules. Sodium hydroxide is also known as caustic soda.

14. The metallic character of __________ is less than that of alkaline earth metals.
a) Boron family
b) Alkali metals
c) Magnesium
d) Hydrogen
Answer: a
Clarification: The elements of the Boron family are less electropositive than the alkaline earth metals due to their smaller size and higher ionization enthalpies. On moving down the group, the electropositive character first increases from Boron to aluminium and then decreases from gallium so thallium due to the presence of d and f orbitals which causes poor shielding.

15. Which of the following is the correct order for the stability of plus one oxidation State?
a) Ga < In < Tl
b) Ga < In > Tl
c) Ga > In < Tl
d) Ga > In > Tl
Answer: a
Clarification: The correct order of the increased stability of + 1 oxidation state in gallium, indium and thallium is that; gallium stability is less than that of indium and indium stability is less than that of thallium.

Chemistry Multiple Choice Questions on “Hydrocarbons – Alkenes”.

1. Alkenes are not called olefins.
a) True
b) False
Answer: b
Clarification: Alkenes are unsaturated noncyclic hydrocarbons which have sp² hybridization with 120-degree bond angle. They are called olefins which mean oil forming and it indicates they are highly reactive nature alkynes general formula is CnH_2n.

2. Ethene is prepared from chloroethane this is an example of a reaction __________
a) from alkynes
b) removal of vicinal dihalides
c) acidic dehydrogenation
d) dehydrohalogenation
Answer: d
Clarification: When chloroethane is heated in the presence of alcoholic potassium Hydroxide, a beta-elimination product is formed, that is ethane, hydrogen, and chlorine are removed which is dehydrohalogenation (the halogen can be either chlorine or bromine or iodine).

3. Alkene __________ in the physical properties of alkanes.
a) there is no comparison
b) differ completely
c) differ in a few aspects
d) same as
Answer: c
Clarification: Alkenes as a class resemble alkanes in physical properties, except in types of isomerism and difference in polar nature. The first three of the series are gases, the next 14 are liquid and the higher members are solids they show a regular increase in boiling point with an increase in size.

4. Alkenes show __________ isomerism.
a) only structural
b) only geometrical
c) both geometrical and structural
d) neither geometrical nor structural
Answer: c
Clarification: Alkynes show both structural isomerism as well as geometrical isomerism, structural isomerism exhibited by alkenes are chain isomerism and position isomerism, while alkenes also exhibit stereoisomerism as geometrical cis-trans isomerism.

5. Addition reaction of hydrogen Bromide to the unsymmetrical alkene follows __________
a) anti markovnikov’s rule
b) markovnikov’s rule
c) kharish effect
d) peroxide effect
Answer: b
Clarification: According to markovnikov’s rule the negative part of the addendum which means adding molecule, gets attached to that carbon atom which possesses less number of hydrogen atoms, it’s the opposite of anti markovnikov’s rule.

6. What is kharash effect?
a) Dehydrogenation
b) Peroxide effect
c) Markovnikov’s rule
d) Addition of hydrogen
Answer: b
Clarification: Anti markownikoff rule is also known as peroxide effect and kharash effect; in the presence of organic peroxide, the addition of only hydrogen Bromide molecule on unsymmetrical alkene, takes place contrary to the markovnikov rule.

7. Which of the following is a Bayer’s reagent?
a) The neutral solution of HCL
b) An alcoholic solution of sodium carbonate
c) An acidic solution of potassium hydroxide
d) An aqueous solution of potassium permanganate
Answer: d
Clarification: The dilute aqueous solution of potassium permanganate is known as Bayer’s reagent. Alkenes decolorize Bayer’s reagent and it is used as a test for unsaturation in alkenes. It is a powerful oxidant as well as a syn-reaction occurs.

8. Which of the following compound is more acidic?
a) Alkane
b) Alkene
c) Alkyne
d) All of them are equally acidic
Answer: c
Clarification: The acidic behavior depends upon the hybridization of the molecule as we know that alkane has sp3 hybridization, alkane has sp² hybridization and alkynes has sp hybridization, due to the higher percentage of s-character, alkyne becomes highly acidic when compared with alkene and alkane.

9. What is the intermediate conformation between eclipsed and staggered?
a) Staggered
b) Skew
c) Eclipse
d) Newman
Answer: b
Clarification: The intermediate conformation between eclipsed and staggered is known as skew and gauche formations. The eclipsed form is least stable but the staggered form is the most stable due to the greater distance between the bond pairs or lesser torsional strain.

10. Which of the following statement is true regarding the reactivity order in order to form alkyl halides?
a) Hydrogen iodide is less than that of hydrogen Bromide
b) Hydrogen Bromide is less than that of HCL
c) HCL is greater than that of hydrogen iodide
d) Hydrogen Bromide is less than that of hydrogen iodide
Answer: d
Clarification: In chemical properties of alkenes, HCL, hydrogen Bromide and hydrogen iodide are added to alkenes to form alkyl halides as per their reactivity order that is; hydrogen iodide’s reactivity is greater than that of hydrogen Bromide and it is greater than that of HCL.

Chemistry Multiple Choice Questions on “Atomic and Molecular Masses”.

1. As, per the current system, carbon-12 has been taken as the standard for measuring atomic masses.
a) True
b) False
Answer: a
Clarification: 1 amu is defined as a mass that is almost equal to one-twelfth of the mass of one carbon – 12 atom. It is a unit to measure atomic and molecular mass. The carbon atom is taken relatively here. And also 1 amu = 1.66056×10^-24 g.

2. What is the mass of hydrogen in terms of amu?
a) 1.0020 amu
b) 1.0180 amu
c) 1.0070 amu
d) 1.0080 amu
Answer: d
Clarification: The mass of a hydrogen atom is 1.6736×10^-24 g. When converted in terms of amu, 1.6736×10^-24 g should be divided by 1.66056×10^-24 g. 1.6736×10^-24 g/1.66056×10^-24 g = 1.0078 amu = 1.008 amu. This the process to measure any atomic mass in amu.

3. What is the abbreviation of amu?
a) Atomic matter unit
b) Atomic mass unified
c) Atomic mass unit
d) At mass unity
Answer: c
Clarification: The Atomic mass unit is a standard unit of mass that measures mass on an atomic or molecular scale. One unit of it is practically equal to 1.66056×10^-24 g. 1 amu is defined as a mass that is almost equal to one-twelfth of the mass of one carbon – 12 atom.

4. Nowadays, “amu” is replaced by ____
a) u
b) g
c) kg
d) am
Answer: a
Clarification: Presently, “amu” has been replaced by “u”. Atomic mass unit is “amu”, but now as it has been changed to “u”, & now known as unified mass. One unified atomic mass unit is the mass of one nucleon and is also equal to 1 g/mol.

5. Calculate the average atomic mass of nitrogen present in the atmosphere?

ISOTOPE	ABUNDANCE	ATOMIC MASS
14N	99.69%	14.0031 amu
15N	0.39%	15.0001 amu

a) 14.007 amu
b) 15.001 amu
c) 14.000 amu
d) 14.0031 amu
Answer: a
Clarification: The formula for finding the average atomic mass of an element is given by Avg. Atomic Mass = ∑Abundance of isotope x Mass of isotope. So for nitrogen, avg atomic mass = 99.69 x 14.0031 + 0.39% x 15.0001 = 14.007.

6. A sample of carbon that contains 70% carbon-12 and 30% carbon-14. What do you think is the average atomic mass of this sample?
a) 14.5
b) 14.14
c) 14
d) 12
Answer: c
Clarification: Given that, carbon-12 is of 70% and carbon-14 is of 30%. In order to find avg atomic mass, you should add the products of multiplications 12 with 70/100 and 14 with 30/100. 12 x 0. 7 = 9.8; 14 x 0.3 = 4.2. Now adding them 9.8 + 4.2 = 14.

7. ______ is the sum of atomic masses of the elements present in a molecule.
a) Average atomic mass
b) Atomic mass
c) Gram formula mass
d) Molecular mass
Answer: d
Clarification: Molecular mass is the sum of atomic masses of the elements present in a molecule. Gram formula mass is the amount of a compound with the exact mass in grams as the formula mass in amu. The standard unit of mass that measures mass on the molecular scale or an atomic scale is “amu”.

8. What’s the molecular mass of carbon dioxide?
a) 43
b) 28
c) 44
d) 40
Answer: c
Clarification: The individual mass of carbon is 12 amu and the individual mass of oxygen is 16 amu. The formula for carbon dioxide is CO₂. Thus one carbon and two oxygens. 12(carbon M.wt) + 2 x 16(oxygen M.wts) = 12 + 32 = 44. Therefore the molecular mass of carbon dioxide is 44.

9. What’s the formula mass of NaCl?
a) 23 u
b) 35.5 u
c) 58 u
d) 58.5 u
Answer: d
Clarification: As Cl in NaCl can’t exist in the solid state, we can only calculate it’s formula mass. the individual mass of sodium is 23 u, whereas that of chlorine is 35.5 u. Together formula mass f Sodium chloride is the sum of individual masses, 23 + 35.5 = 58.5 u.

10. Calculate the molecular mass of sucrose(C₁₂H₂₂O₁₁) molecule?
a) 342 amu
b) 343 amu
c) 341 amu
d) 340 amu
Answer: a
Clarification: The individual mass of carbon is 12 amu, the individual mass of hydrogen is 1 amu & the individual mass of oxygen is 16 amu. But sucrose has 12 carbons, 22 hydrogens and 11 oxygens, that is 12 x 12 + 22 x 1 + 11 x 16 = 342 amu.