Category: Class 11 Chemistry Objective Questions

Chemistry Questions and Answers for Entrance exams on “Percentage Composition”.

1. A _______ formula represents a whole number ratio to the simplest form.
a) Molecular
b) Empirical
c) Simpler
d) Shorter
Answer: b
Clarification: An empirical formula is the simplest whole number ratio of various atoms present in a compound. The molecular formula is the exact number of different types of atoms present in the molecule of a compound.

2. Even without knowing the mass percent of each element, we can calculate the empirical formula.
a) True
b) False
Answer: b
Clarification: One must know the mass percent of each and every element of a compound to calculate an empirical formula. As an empirical formula is the simplest whole number ratio of various atoms present in a compound.

3. __________ formula can be calculated if the molar mass is known after having an empirical formula.
a) Molecular
b) Empirical
c) Simpler
d) Shorter
Answer: a
Clarification: The molecular formula is the exact number of different types of atoms present in the molecule of a compound. An empirical formula is the simplest whole number ratio of various atoms present in a compound. Therefore we can calculate the molecular formula if the molar mass is known.

4. Which of the following is an empirical formula?
a) C₆H₁₂O₆
b) H₂O₂
c) CH₄
d) C₂H₆
Answer: c
Clarification: An empirical formula is the simplest whole number ratio of various atoms present in a compound. Only CH₄ has satisfied the conditions of an empirical formula as it is the simplified whole number ratio compound.

5. The molecular formula of a compound is C₆H₁₂O₆. What’s the empirical formula for this compound?
a) C₆H₁₂O₆
b) CHO
c) C₂H₆O₂
d) CH₂O
Answer: d
Clarification: In the molecular formula of glucose that is C₆H₁₂O₆, the carbon, hydrogen, and oxygen are in the ratio of 6:12:6 respectively. So by simplifying them into simpler whole numbers, we obtain 1:2:1. Therefore the empirical formula is CH₂O.

6. A compound consists of 52.17% of carbon, 13.04% of hydrogen and 34.78% of oxygen. Find the molecular formula if the given molecular weight of the compound is 46g.
a) C₂H₅OH
b) C₂H₆
c) C₆H₁₂O₆
d) CH₂O
Answer: a
Clarification: As per the above question, the compounds consist of carbon, hydrogen, and oxygen in the ratio of 52.17:13.04:34.78 respectively. Now multiply the ratio with the molecular mass that is 46 g. Hence we obtain it as 2400:600:1600 that is 24:6:16 (2 atoms of carbon + 6 atom of hydrogen + 1 atom of oxygen). The required compound is C₂H₅OH.

7. Which of the following cannot be a molecular formula for an empirical formula HO?
a) H₂O
b) H₂O₂
c) HO
d) HO₂
Answer: b
Clarification: The molecular formula is the exact number of different types of atoms present in the molecule of a compound. The rest compounds are not in the same ratio as of empirical formula ones. Though HO is possible, it can’t exist.

8. In glucose simplest ratio between C, H and O is ________
a) 6:12:6
b) 3:4:3
c) 1:2:1
d) 2:3:2
Answer: c
Clarification: the molecular formula of glucose is C₆H₁₂O₆. The ratio in the molecular formula is 6:12:6; carbon, hydrogen, and oxygen respectively. So by simplifying them into simpler whole numbers, we obtain 1:2:1.

9. Which of the following is true regarding molecular formula?
a) actual whole numbered ratio
b) rational numbered ratio
c) simplest possible whole numbered ratio
d) the same as the empirical ratio
Answer: a
Clarification: Actual whole numbered ratio is correct because the molecular formula is the exact number of different types of atoms present in the molecule of a compound. Rational may be fractional or decimal, simplest possible whole numbered is empirical.

10. Which of the following cannot be an empirical formula?
a) NH₃
b) C₅H₁₀
c) H₂O
d) NaCl
Answer: b
Clarification: C₅H₁₀ cannot be an empirical formula because of the carbon and hydrogen ratio in this compound is 5:10 respectively. They are not in the simplest possible whole numbered ratio (1:2 is the simplest for this compound). Hence it cannot be an empirical compound.

Chemistry for Entrance exams,

Chemistry Multiple Choice Questions on “Bond Parameters”.

1. Which of the following cannot be used to measure bond lengths?
a) Spectroscopy
b) X-ray diffraction
c) Electron diffraction
d) Young’s Double-slit method
Answer: d
Clarification: The equilibrium distance between the nuclei of two bonded atoms in a molecule is known as bond length. It can be measured by spectroscopy, X-ray diffraction, and electron diffraction. Young’s double slit method is used for determining electromagnetic spectra.

2. The covalent radius in a chlorine molecule and van der Waal’s radius between chlorine molecules respectively can be ________ & _________
a) 99pm, 198pm
b) 198pm, 99pm
c) 198pm, 198pm
d) 99pm, 99m
Answer: a
Clarification: The half of the distance between two covalently bonded similar atoms in the same molecule is called covalent radius, whereas the half of the distance between two similar atoms of different molecules in a solid is known as van der Waal’s radius. Therefore covalent radius is smaller than the van der Waal’s radius.

3. What are the units of measuring the bond angle?
a) meters
b) kilograms
c) degree
d) mole
Answer: c
Clarification: The angle between two bonds from the same atom that is bonded to different atoms is called the bond angle. It expressed in the units of degree experimentally by spectroscopic methods. It depicts the shape of the molecule in a 3D dimension.

4. The bond angle between the hydrogen atoms is _________
a) 104.5°
b) 104°
c) 105.4°
d) 105°
Answer: a
Clarification: The water molecule is the V-shape, so the angle between hydrogen through oxygen is given → by 104.5°. As we know the angle between two bonds from the same atom that is bonded to different atoms is called the bond angle.

5. Strength of the bond between the two atoms can be known from bond dissociation enthalpy.
a) True
b) False
Answer: a
Clarification: Yes, it’s true. The energy that is used to break a molecule into atoms is bond dissociation enthalpy. The higher the bond dissociation energy, the stronger the bond between the atoms. So the strength of the bond between the two atoms can be known from bond dissociation enthalpy.

6. The bond enthalpy of H₂O and OH are 502 KJ mol^-1 and 427 KKJ mol^-1. Then what is the average bond enthalpy?
a) 502 KJ mol^-1
b) 464.5 KJ mol^-1
c) 427 KJ mol^-1
d) 75 KJ mol^-1
Answer: b
Clarification: We know that H₂O_(g) → H_(g) + OH_(g); ΔH₁ = 502 kJ mol^-1 and OH_(g) → H_(g) + O_(g); ΔH₂ = 427 kJ mol^-1. So the average bond enthalpy is given by their mean that is 427 + 502/2 = 464.5 KJ mol^-1. This method is used for polyatomic molecules like water.

7. What is the bond order of CO?
a) 3
b) 2
c) 1
d) 4
Answer: a
Clarification: The number of bonds that are created between two atoms in a molecule is the bond order of that bond. The molecule carbon monoxide CO has a triple bond between the carbon and oxygen, so it’s bond order is 3.

8. All the __________ species(molecules and ions) have the same bond order.
a) isotopic
b) isoelectronic
c) isobaric
d) isoneutronic
Answer: b
Clarification: The molecules and ions that contain the same number of electrons are called isoelectronic species. They all have the same bond order. For example, the molecules and ions like N₂, CO and NO⁺ have the bond order 3 and 14 electrons.

9. Resonance does stabilize the molecule.
a) False
b) True
Answer: b
Clarification: Resonance stabilizes the molecule as the resonance hybrid comprises of less energy than other canonical structures. Resonance is made of many structures that change frequently in molecules in order to maintain stability in the molecule.

10. Which of the following molecules may have a dipole movement?
a) N₂
b) CH₄
c) BeF₂
d) H₂O
Answer: d
Clarification: The dipole movement is given by the product of charge and the distance of separation between atoms. It is expressed in Debye units (D). For the molecules N₂, CH₄ and BeF₂ the net dipole movement is zero as they cancel each other due to symmetry. But water molecule due to its V-shape exhibits dipole movement.

Chemistry written test Questions & Answers on “Equilibrium in Physical Processes”.

1. If both the forward and reverse reaction rates are equal in the equilibrium is said to be ____________
a) dynamic equilibrium
b) equilibrium mixture
c) static equilibrium
d) newton equilibrium
Answer: a
Clarification: When the reactants are kept in a closed vessel at a certain temperature the concentration of reactants keep on decreasing while the concentration of products keep on increasing, at this stage when the rate of both the forward and the reverse reactions become equal, it is said to be in a dynamic equilibrium.

2. Physical equilibrium is the same as the chemical equilibrium.
a) true
b) false
Answer: b
Clarification: Equilibrium that is set up in a physical process like the evaporation of water melting of solids is called physical equilibrium. If a reversible reaction is carried out in a closed vessel chemical equilibrium occurs when the rate of both the forward and backward reactions are equal, so the above statement is false.

3. Which of the following characteristics of chemical equilibrium is true?
a) equilibrium is dynamic in nature
b) equilibrium cannot be attained from either side
c) equilibrium cannot be obtained in a closed container
d) equilibrium state is affected by the presence of a catalyst
Answer: a
Clarification: The correct statements of the wrong ones are; equilibrium can be attained from another side, the catalyst does not affect the equilibrium state and it can only be achieved in a closed container. Therefore equilibrium is dynamic in nature is the true characteristic of chemical equilibrium in the given options.

4. Which of the following is an example of solid-liquid equilibrium?
a) water and steam at hundred degrees centigrade
b) water and ice at 0-degree centigrade
c) the point where Ammonia is sublimized
d) boiling point of water
Answer: b
Clarification: At zero degree centigrade, when water and ice are together the opposing process occurs simultaneously at the same rate, so the amount of Ice and water remains constant. It is an example of a solid-liquid equilibrium.

5. Amount of a gas that is dissolved in a solvent depends on the pressure of the solvent.
a) True
b) False
Answer: a
Clarification: The most common form of Henry’s law states that the partial pressure of the gas in the vapor phase is proportional to the mole fraction of the gas in a solution, therefore we can say that the above-given statement is true.

6. Which of the following statements is false regarding the equilibrium constant?
a) it has a definite value for every chemical reaction at a particular temperature
b) it is independent of initial concentrations of the reactants
c) it is dependent on the presence of a catalyst
d) if K is the equilibrium constant for a backward reaction then the forward reaction’s equilibrium constant is 1/k
Answer: c
Clarification: Equilibrium constant is independent of the presence of a catalyst, so the statement regarding the catalyst is wrong. A catalyst helps reaction to attain its equilibrium faster but does not alter the equilibrium constant.

7. What will happen if the rate of evaporation is equal to the rate of condensation in the water?
a) solid-liquid equilibrium
b) liquid-vapor equilibrium
c) solid-vapor equilibrium
d) melting
Answer: b
Clarification: When the rate of evaporation is equal to the rate of condensation water in the liquid phase and steam in vapor phase remained at equilibrium because its forward rate of the reaction and the backward rate of the reaction is the same at this particular temperature.

8. The equilibrium in a chemical reaction is represented by the symbol ____________
a) ↠
b) (Leftarrow)
c) (rightleftharpoons)
d) →
Answer: c
Clarification: The symbol that has both the left-sided harpoon and right-sided harpoon together is a symbol used for the equilibrium in a chemical reaction. It denotes that the backward and the forward rates are equal and is represented by the symbol “(rightleftharpoons)”.

9. Select the correct equilibrium involving physical equilibrium.
a) it is possible only in a closed system at a given temperature
b) both forward and backward does not occur at the same rate
c) there is a dynamic but an unstable condition
d) measurable properties of the system do not remain constant
Answer: a
Clarification: The corrected statements of the wrong ones are that both backward and forward reactions occur at the same rate in a stable condition, while the measurable properties of the system remain constant.

10. When solid sugar dissolves in the solution __________ equilibrium is attained.
a) liquid vapor
b) solid liquid
c) solid vapor
d) no
Answer: b
Clarification: When sugar, which is in solid form dissolves in a solvent, forming sugar solution – a solid-liquid equilibrium is formed, where the rate of dissolution of sugar is equal to the rate of crystallization of sugar.

To practice all written questions on Chemistry,

Chemistry Multiple Choice Questions on “Position of Hydrogen in the Periodic Table”.

1. The element that is known as Rogue element is ________
a) beryllium
b) hydrogen
c) helium
d) lithium
Answer: b
Clarification: Hydrogen resembles with alkali metals as well as halogens at the same time it differs from both and certain characteristics, that is why hydrogen is called a Rogue Element. Finally, it’s been placed in the first group.

2. Which of the following element is an alkali as well as halogen?
a) hydrogen
b) sodium
c) chlorine
d) magnesium
Answer: a
Clarification: Hydrogen is an alkali metal as well as a halogen because of its outer shell configuration as well as its high electronegative character, no other element has a type of duel characteristic in the periodic table.

3. Which of the following is hydrogen’s electronic configuration?
a) 1s¹
b) 1s²
c) 2s¹
d) 2s²
Answer: a
Clarification: The electronic configuration of hydrogen is 1s¹, as it has only one Proton. It belongs to the first group and is ready to gain one electron in order to become a noble gas like helium which is next to it.

4. The atomic number of hydrogen is 1.
a) true
b) false
Answer: a
Clarification: Atomic number of an element represents the number of protons in that particular element. Here as hydrogen has only one Proton, its atomic number is considered to be one, so the above statement is true.

5. Hydrogen is a ___________________
a) metal
b) metalloid
c) non-metal
d) solid
Answer: c
Clarification: Hydrogen is a nonmetal denoted by the symbol “H”, but it is placed in the first group, which consists of metals. This is because of the outer shell configuration of hydrogen and that it’s valency is 1. It’s highly electronegative in nature.

6. Hydrogen is the 1st element. The elements in the periodic table are arranged with respect to their __________
a) atomic numbers
b) molecular weights
c) atmospheric abundance
d) physical state
Answer: a
Clarification: We all know that the elements in the periodic table are arranged according to their atomic numbers and atomic numbers are nothing but the number of protons in that element. So hydrogen takes the first place.

7. Hydrogen has _____________ ionization enthalpy.
a) high
b) low
c) zero
d) no
Answer: a
Clarification: Though hydrogen is placed in the first group which is of alkali metals, it has a very high ionization enthalpy this is because it has a characteristic of a halogen as well. We can say that hydrogen is an alkali metal and a halogen at a time.

8. The property of hydrogen of forming diatomic molecule is from ______________
a) halogen
b) alkali metal
c) noble gas
d) d-block
Answer: a
Clarification: As we know that hydrogen is an alkali metal as well as a halogen. It has properties of both alkali metals and halogens, the property of formation of a diatomic molecule is from halogens, but not from alkali metals.

9. H⁺ Ion exist freely.
a) true
b) false
Answer: b
Clarification: The loss of electrons from hydrogen atom results in the hydrogen nucleus that is H⁺ of the size 1.5 x 10^-3 pm and it is extremely small when compared to a normal at atomic and ionic sizes that are around 50 to 200 pm.

10. Reactivity of hydrogen is ______________ compared to halogens.
a) high
b) low
c) zero
d) negative
Answer: b
Clarification: Though hydrogen has many properties of halogens, in terms of reactivity it shows very low similarity when compared to halogens. This is one of the reasons, it’s probably not placed in halogens, but in alkali metals.

This set of Chemistry Question Papers for NEET Exam on “p-Block Elements – Uses of Boron and Aluminium and their Compounds”.

1. What is ammonal?
a) a mixture of aluminium powder with ammonium nitrite
b) a mixture of aluminium powder with ammonium nitrate
c) a mixture of aluminium powder with ammonium sulphate
d) a mixture of aluminium powder with ammonium chloride
Answer: b
Clarification: A mixture of aluminium powder with ammonium nitrate is called ammonal and is used in bombs with a ratio of 5:95. Here the aluminium acts as a fuel and ammonium nitrate as an oxidizer, it was first used in the year 1916 by the britishers near mines.

2. Which of the following material is used for making fireproof clothes?
a) Aluminium chloride
b) Aluminium oxide
c) Aluminium nitrate
d) Aluminium sulphate
Answer: d
Clarification: Aluminium sulphate which is given by the chemical formula Al₂(SO₄)₃ is used for making fireproof clothes and it is also used as a fire fighting foam. Aluminium sulphate is also used as an antiseptic, astringent and also as a modern in dyeing textiles.

3. Which of the following is not a use of Boron?
a) silver paints
b) bulletproof vest
c) in nuclear reactors
d) making of boron fibres
Answer: a
Clarification: There are many applications of boron like heat resistant glasses, glass wool, fibreglass, flux for soldering metals, for heat, scratch and stain resistant glazed coating to earth and wears and as a constituent of medical soaps. It is also used and the making of Boron fibres, bulletproof vest making and also and nuclear reactions in order to absorb neutrons.

4. Boron is used as a ______________
a) double insulator
b) semiconductor
c) insulator
d) conductor
Answer: b
Clarification: Yes, Boron is used as a semiconductor and also Boron Steel rods are used for controlling the nuclear reactions. Boron is used as a dopant for semiconductors such as Silicon and Germanium. Pure Boron is a black, lustrous semiconductor.

5. Which of the following is not a use of orthoboric acid?
a) painting
b) antiseptic
c) eye lotion
d) food preservative
Answer: a
Clarification: Orthoboric acid which is given by the chemical formula H3BO₃ is used as an antiseptic and eye lotion under the name boric lotion and it is also used as a food preservative. The boric lotion is a saturated solution of 4% boric acid in water.

6. Which of the following is used as a catalyst in Friedel craft reaction?
a) cement
b) boron
c) anhydrous aluminium chloride
d) borax
Answer: c
Clarification: Friedel crafts reactions are the reactions in which substituents are added to the aromatic rings. There are two types of friedel craft reactions namely alkylation and acylation. Anhydrous aluminium chloride is used as a catalyst in these Friedel craft reactions.

7. What is the chemical formula of alumina and anhydrous aluminium chloride?
a) Al₂O₃, AlCl
b) Al₂O₃, AlCl₃
c) Al₂O, AlCl₃
d) AlO₃, AlCl₃
Answer: b
Clarification: The chemical formula of alumina is Al₂O₃ and that of anhydrous aluminium chloride is AlCl₃. Alumina is nothing but aluminium oxide. Anhydrous aluminium chloride is prepared by heating a mixture of alumina and carbon in a current of dry chlorine.

8. Aluminium oxide as otherwise called as ______________
a) aluminium sulphate
b) alumina
c) alum
d) aluminium
Answer: b
Clarification: Alumina is also known as aluminium oxide and it is the most stable compound of aluminium that occurs in nature as colourless corundum and several coloured oxides, like ruby, topaz, sapphire, and emerald, these are used as precious stones.

9. Alum is a double sulphate.
a) true
b) false
Answer: a
Clarification: The term alum is given to double sulphates of the type X₂SO₄.Y₂(SO₄)₃.24H₂O where, X represents a monovalent cation such as sodium ion, potassium ion and ammonium while why is a trivalent cation such as aluminium 3 +, chromium 3 +, ferrous 3 + and Cobalt 3 +. Lithium-ion does not form alum.

10. Which of the following is not an alum?
a) covalent alum
b) Potash alum
c) ammonium alum
d) sodium alum
Answer: a
Clarification: K₂SO₄.Al₂(SO₄)₃.24H₂O, Na₂SO₄.Al₂(SO₄)₃.24H₂O, (NH₄)₂SO₄.Al₂(SO₄)₃.24H₂O and (NH₄)₂SO₄.Fe₂(SO₄)₃.24H₂O are respective chemical formulae of Potash alum, sodium alum, ammonium alum and ferric alum.

To practice Chemistry Question Papers for NEET Exam,

Chemistry Multiple Choice Questions on “Environmental Pollution”.

1. A substance, which causes pollution, is known as which of the following?
a) Pollutant
b) Carcinogen
c) Polluting element
d) Irritant
Answer: a
Clarification: A substance, causing pollution, is called as a pollutant. Pollutants can be solid, liquid, or gaseous substances present in greater concentrations than in natural abundance and are produced due to human activities or due to natural happenings. Carcinogens are substances, if exposed to, which can cause cancer. Irritants normally cause irritations to skin.

2. Identify the degradable pollutant from the following.
a) Chemicals
b) Metals
c) Discarded vegetables
d) Plastic
Answer: c
Clarification: Discarded vegetables are degradable pollutants. Since they are organic, they can be rapidly broken down by micro-organisms through natural processes. Chemicals, metals, and plastics are inorganic and they will slowly degrade, thereby, remaining in an unchanged form in the environment for many decades.

3. What is the full form of DDT?
a) Diphenyldichlorotrichloroethane
b) Dichlorodiphenyltrichloroethane
c) Dichlorodiphenyltriphenylethane
d) Dichlorodiphenyltrichloroethene
Answer: b

Clarification: The full form of DDT is dichlorodiphenyltrichloroethane. It is a colorless, tasteless, and almost odorless crystalline chemical compound. It was originally developed as an insecticide, but then, its use was stopped due to its harmful effect on environment as well as on the living organisms. If exposed to high concentrations, it can cause vomiting, seizures or tremors in human beings.