**Some Basic Concepts of Chemistry Class 11 – MCQs (Answers)**

**Ans 1.**

**Ans 2.** 6.023 × 10^{23} has four significant figures. The total number of digits in a number including the last digit whose value is uncertain is called the number of significant figures.

**Ans 3. **All non-zero digits are significant. Hence, there are 6 significant figures in 10.3406 g.

**Ans 4. **0.02856 × 298.15 × 0.112 /0.5785

**Ans 5.** Precision refers to the closeness of various measurements for the same quantity. Accuracy is the agreement of a particular value to the true value of the result. Thus, A and B are precision and accuracy respectively.

**Ans 6. **As we know, the least count of an instrument is equal to the most possible error of the instrument, hence most possible error of the instrument will be 0.01 cm.

**Ans 7. **All the given statements are correct about molecular mass.

**Ans 8. **Molecular mass of urea (NH_{2}CONH_{2}) is

= 2 × (Atomic mass of N) + 4 × (Atomic mass of H) + (Atomic mass of C) + (Atomic mass of O) = 60

Mass percentage of N = (28/60) × 100 = 46.67 %

**Ans 9.**

**Ans 10. **One mole of any substance contains 6.022 × 10^{23} atoms/ molecules. Hence, the number of millimoles of H_{2}SO_{4 }= Molarity × Volume (in mL) = 0.02 × 100 = 2 × 10^{−3} mol

Number of molecules = number of moles × N_{A}

= 2 × 10^{−3} × 6.022 × 10^{23 }= 12.044 × 10^{20} molecules

**Ans 11.** In 18 g of water, the number of H_{2}O molecules is N_{A} .

18 mg of water, the number of H_{2}O molecules would be =

= 10^{-3} × N_{A}

**Ans 12. **As 22400 mL water contains water molecules = 6.023 × 10^{23} molecules

**Ans 13.**

**Ans 14.**

**Ans 15. **Molecular mass of CO_{2} = 1 × 12 + 2 × 16 = 44 g

1 g molecule of CO_{2} contains 1 g atoms of carbon

؞ 44 g of CO_{2} contain C = 12 g atoms of carbon

% of C in CO_{2} = 12/44 × 100 = 27.27 %

Some Basic Concepts of Chemistry Class 11

**Ans 16.**

**Ans 17.**

**Ans 18. **2Na_{2}HPO_{4} + NaH_{2}PO_{4} + 2(NH_{2})_{2} CO → Na_{5}P_{3}O_{10} + 4NH_{3} + 2CO_{2}

Hence, the stoichiometric ratio of sodium dihydrogen orthophosphate and sodium hydrogen orthophosphate is 2:1

**Ans 19. **The molar mass of sulphuryl chloride is 32 + 16 + 16 + 35.5 + 35.5 = 135 g/mol

The number of gram molecules in 13.5 g of sulphuryl chloride is = 13.5/135 = 0.1 mol

**Ans 20.** One litre of the solution

**Ans 21.** (e) the assertion is false but the reason is true

**Ans 22.** (e) the assertion is false but the reason is true

**Ans 23. **(c) the assertion is true but the reason is false.

**Ans 24. **(e) the assertion is false but the reason is true

**Ans 25. **(e) the assertion is false but the reason is true

Some Basic Concepts of Chemistry Class 11