Chemistry MCQs for Class 11 Chapter 1 Some Basic Concepts of Chemistry

Q.1. Which one of the following sets of compounds correctly illustrate the law of reciprocal proportions?
(a) P2O3, PH3, H2O
(b) P2O5, PH3, H2O
(c) N2O5, NH3, H2O
(d) N2O, NH3, H2O

Answer (a) In law of reciprocal proportions, the two elements combining with the third element, must combine with each other in the same ratio or multiple of that ratio. P2O3, PH3, and H2O correctly illustrate the law of reciprocal proportions. Ratio in the number of atoms of hydrogen and oxygen combining with one P is 3 : 1.5 i.e., 2 : 1.

Q.2. If we consider that 1/6, in place of 1/12, mass of carbon atom is taken to be the relative atomic mass unit, the mass of one mole of a substance will
(a) decrease twice
(b) increase two fold
(c) remain unchanged
(d) be a function of the molecular mass of the substance

Answer (a)

Q.3. The maximum number of molecules are present in
(a) 15 L of H2 gas at STP
(b) 5 L of N2 gas at STP
(c) 0.5 g of H2 gas
(d) 10 g of O2 gas

Answer (a)

Q.4. How many moles of magnesium phosphate, Mg3(PO4)2 will contain 0.25 mole of oxygen atoms?
(a) 1.25 × 10–2
(b) 2.5 × 10–2
(c) 0.02
(d) 3.125 × 10–2

Answer (d)

Q.5. The mass of BaCO3 produced when excess CO2 is bubbled through a solution of 0.205 mol Ba(OH)2 is :
(a) 81 g
(b) 40.5 g
(c) 20.25 g
(d) 162 g

Answer (b)

Q.6. For the reaction Fe2O3 + 3CO2 → 2Fe + 3CO2, the volume of carbon monoxide required to reduce one mole of ferric oxide is
(a) 67.2 dm3
(b) 11.2 dm3
(c) 22.4 dm3
(d) 44.8 dm3

Answer (a)

Q.7. How many moles of lead (II) chloride will be formed from a reaction between 6.5 g of PbO and 3.2 g of HCl ?
(a) 0.044
(b) 0.333
(c) 0.011
(d) 0.029

Answer (d)

Q.8. The increasing order of molarity with 25 gm each of NaOH, LiOH, Al(OH)3, KOH, B(OH)3 in same volume of water?
(a) Al(OH)3 < B(OH)3 < KOH < NaOH < LiOH
(b) LiOH < NaOH < KOH < B(OH)3 < Al(OH)3
(c) LiOH < NaOH < B(OH)3 < KOH < Al(OH)3
(d) NaOH < LiOH < B(OH)3 < Al(OH)3 < KOH

Answer (a)

Q.9. Which of the following statements about a compound is incorrect?
(a) A molecule of a compound has atoms of different elements.
(b) A compound cannot be separated into its constituent elements by physical methods of separation.
(c) A compound retains the physical properties of its constituent elements.
(d) The ratio of atoms of different elements in a compound is fixed.

Answer (c)

Q.10. Which has highest weight ?
(a) 1 m3 of water
(b) A normal adult man
(c) 10 litre of Hg
(d) All have same weight

Answer (a)

Q.11. The number of significant figures for the three numbers 161 cm, 0.161 cm, 0.0161 cm are
(a) 3,4 and 5 respectively
(b) 3,4 and 4 respectively
(c) 3,3 and 4 respectively
(d) 3,3 and 3 respectively

Answer (d)

Q.12. The correctly reported answer of addition of 29.4406, 3.2 and 2.25 will have significant figures
(a) 3
(b) 4
(c) 2
(d) 5

Answer (a)

Q.13. The percentage of copper and oxygen in samples of CuO obtained by different methods were found to be the same. This illustrate the law of
(a) constant proportions
(b) conservation of mass
(c) multiple proportions
(d) reciprocal proportions

Answer (a)

Q.14. Which one of the following pairs of compounds illustrate the law of multiple proportions ?
(a) H2O and Na2O
(b) MgO and Na2O
(c) Na2O and BaO
(d) SnCl2 and SnCl4

Answer (d)

Q.15. 10 dm3 of N2 gas and 10 dm3 of gas X at the same temperature contain the same number of molecules, the gas X is
(a) CO2
(b) CO
(c) H2
(d) NO

Answer (b)

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