250+ TOP MCQs on Percentage Composition and Answers

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.

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