UP Board Class 9 Science Chapter 3 Atoms And Molecules Multiple Choice Questions

Atoms And Molecules Multiple Choice Questions

Question 1. A sample of pure water, irrespective of its source, contains 11.1% hydrogen and 88.9% oxygen. The data supports

1. Law of multiple proportions
2. Law of reciprocal proportions
3. Law of constant proportions
4. Law of conservation of mass

Answer: 3. law of constant proportions

Water obtained from any source contains hydrogen and oxygen in the same proportion by mass. Hence, the data supports the law of constant proportion.

Question 2. If 12 g of C is burnt in the presence of 32 g of O₂, how much CO₂ will be formed?

1. 40 g CO₂
2. 44 g CO₂
3. 30 g CO₂
4. 22 g CO₂

Answer: 2. 44 g CO₂

CO₂ is formed by the following reaction.

⇒ \(\underset{12 \mathrm{~g}}{\mathrm{C}}+\underset{32 \mathrm{~g}}{\mathrm{O}_2} \longrightarrow \mathrm{CO}_2\)

By the law of conservation of mass,

Mass of reactants = Mass of products

Mass of C+ Mass of O₂ = Mass of CO₂

12 g + 32 g = 44 g

Therefore, 44 g of CO₂ will be formed.

Question 3. The formula of chloride of a metal M is MCl₃, then the formula of the phosphate of metal M will be

1. M₂PO₄
2. MPO₄
3. M₂(PO₄)₃
4. M₃PO₄

Answer: 2. MPO4

The valency of M is +3

∴ The formula of phosphate of metal M will be MPO₄.

Question 4. How many moles are present in 11.5 g of sodium?

1. 0.5 mol
2. 5.0 mol
3. 0.05 mol
4. 1.5 mol

Answer: 1. 0.5 mol

23 g of Na present in = 1 mol

11.5 g of Na present = \(\frac{1}{23} \times 11.5\)

= 0.5 mol.

Question 5. Which one of the following statements is true?

1. Mass of 0.5 mole of N₂ gas > mass of 0.5 mole of N atoms
2. Mass of 0.5 mole of N₂ gas =mass of 0.5 mole of O₂ gas
3. Mass of 0.5 mole of N₂ gas < mass of 0.5 mole of N atoms
4. Mass of 0.5 mole of N₂ gas = mass of 0.5 mole of N atoms

Answer: 1. Mass of 0.5 mole of N₂ gas > mass of 0.5 mole of N atoms

1. 1 mole of N₂ gas has mass = 28 g
2. 0.5 mole of N₂ gas has mass = 28 × 0.5 =14 g
3. 1 mole of N atoms have mass = 14 g
4. 0.5 mole of N atoms have mass =14 × 0.5 = 7g

∴ Mass of 0.5 mole of N₂ gas > mass of 0.5 mole of N atoms.

Question 6. Which of the following represents 1 amu?

1. Mass of hydrogen molecule 1
2. \(\frac{1}{12}\)th of mass of C-12 atom 12
3. Mass of 0-12 atom
4. Mass of C-12 atom

Answer: 2. \(\frac{1}{12}\)th of mass of C-12 atom 12

Question 7. A 0.24 g sample of a compound of oxygen and boron was found by analysis to contain 0.096 g of boron and 0.144 g of oxygen.

What will be the percentage composition of the compound by weight?

1. Boron = 40%, oxygen = 60%
2. Boron = 60%, oxygen = 40%
3. Boron = 35%, oxygen = 55%
4. Boron = 20%, oxygen = 30%

Answer: 1. Boron = 40%, oxygen = 60%

We know that the mass % of any element in a compound

⇒ \(\frac{\text { mass of element }}{\text { mass of compound }} \times 100\)

⇒ \(\text { Mass } \% \text { of boron }=\frac{0.096}{0.24} \times 100=40 \%\)

⇒ \(\text { Mass } \% \text { of oxygen }=\frac{0.144}{0.24} \times 100=60 \%\)

Question 8. Calculate the molecular mass of Al₂(SO₄)₃.

1. 342 u
2. 242 u
3. 249.5 u
4. 288 u

Answer: 1. 342 u

The molecular mass of Al, (SO₄)₃

= 2 × Atomic mass of Al + 3 [Atomic mass of S + 4 × (Atomic mass of O)]

= 2 × 27. 0 u + 3 × (32. 0 u + 4 × 16.0 u)

= 54 u + 3(32 + 64)u = 54 + 3 × 96u

= 54 + 288 u =342u

Question 9. What will be the mass of 5 mole of SO₂?

1. 310 g
2. 320 g
3. 290 g
4. 120 g

Answer: 2. 320 g

Molecular mass of SO₂ = 64 g

⇒ \(\text { Number of mole }=\frac{\text { Mass of } \mathrm{SO}_2(\mathrm{~g})}{\text { Molecular mass of } \mathrm{SO}_2(\mathrm{~g})}\)

Mass of SO₂ (g) = number of mole x molecular mass of SO₂

= 5 × 64

= 320 g

Question 10. Calculate the mass in g of 2NA molecules of CO₂,

1. 88g
2. 22g
3. 44g
4. None of these

Answer: 1. 88g

NA molecules of CO₂ have molecular mass =44 g.

∴ 2 N A molecules of CO₂ have a molecular mass

= 44 x 2 = 88 g

Question 11. How many molecules are in 5.23 g of glucose (C₆H₁₄O₆)?

1. 1.75 x 10²¹
2. 1.75 x 10²²
3. 1.65 x 10²²
4. None of the above

Answer: 2. 1.75 x 10²²

180g glucose has =NA molecules.

∴ 5.23 g glucose has = \(\frac{5.23 \times 6.022 \times 10^{23}}{180}\)

= 1.75 x 10²² molecules.

Question 12. “Mass can neither be created nor destroyed in a chemical reaction” is defined

1. Law of constant proportion
2. Law of conservation of mass
3. Law of reciprocal proportions
4. Law of multiple proportions

Answer: 2. Law of conservation of mass

Question 13. The percentage of copper and oxygen in samples of CuO obtained by different methods was found to be the same. They illustrate the law of

1. Conservation of mass
2. Multiple proportions
3. Constant proportion
4. Reciprocal proportion

Answer: 3. Constant proportion

Question 14. The percentage of hydrogen in H₂O is

1. 11.12
2. 21.12
3. 20.60
4. 80.0

Answer: 1. 11.12

Question 15. The mass of one C atom is

1. 6.022 × 10²³g
2. 12g
3. 6 g
4. 1.99 × 10^-23g

Answer: 4. 1.99 × 10^-23g

Question 16. The correct symbol for silver is

1. Ag
2. Au
3. A1
4. Si

Answer: 1. Ag

Question 17. The chemical symbol P stands for

1. Phosphorus
2. Potassium
3. Polonium
4. Platinum

Answer: 1. Phosphorus

Question 18. Adding electrons to an atom will result in a

1. Anion
2. Cation
3. Molecule
4. Salt

Answer: 3. Molecule

Question 19. One gram of which of the following contains the largest number of oxygen atoms?

1. O₃
2. O
3. O₂
4. All contain same

Answer: 1. O₃

Question 20. How many molecules are present in one gram of hydrogen?

1. 6.02 × 10²³
2. 1.5 × 10²⁴
3. 3.01 × 10²³
4. 4.5 × 10²³

Answer: 3. 3.01 × 10²³

Question 21. Find out the molecular mass of H₂O.

1. 16μ
2. 18μ
3. 24μ
4. 72μ

Answer: 2. 18μ

Question 22. Write down the names of compounds represented by the following formulae.

1. Al₂ (SO₄)₃
2. CaCl₂
3. K₂SO₄
4. KNO₃
5. CaCO₃

Answer:

1. Aluminium sulphate [Al₂(SO₄)₃]
2. Calcium chloride (CaCl₂)
3. Potassium sulphate (K₂SO₄)
4. Potassium nitrate (KNO₃)
5. Calcium carbonate (CaCO₃)

Question 23. What is meant by the term chemical formula?

1. Al₂(SO₄)₃
2. CaCl
3. K2SO₄
4. KNO₃
5. CaCO₃

Answer:

1. OD Aluminium sulphate [Al₂(SO₄)₃]
2. Calcium chloride (CaCl₂)
3. Potassium sulphate (K₂SO₄)
4. Potassium nitrate (KNO₃)
5. Calcium carbonate (CaCO₃)

Atoms And Molecules Fill In The Blanks

Question 1. In a chemical reaction, the sum of the masses of the reactants and products remains unchanged. This is called___
Answer: The law of conservation of mass

Question 2. A group of atoms carrying a fixed charge on them is called___
Answer: Polyatomic ion

Question 3. The formula unit mass of Ca₃(PO₄)₂ is___
Answer: 310 u

Question 4. The formula of sodium carbonate is … and that of ammonium sulphate is ___
Answer: Na₂CO₃; (NH₄)₂SO₄