An element X occurs naturally as three isotopes with the following abundances:

²⁰⁰X = 90%, ¹⁹⁹X = 8%, and ²⁰²X = 2%.

What is the approximate average atomic mass of element X?

1.	205 u	2.	220 u
3.	196 u	4.	200 u

Calculate the change in volume when 100 mL of phosphine ( PH₃) decomposes completely into phosphorus and hydrogen.

Calculate the total molarity of all the ions present in a solution containing 0.1 M of CuSO₄ and 0.1 M of Al₂(SO₄)₃.

1. 0.2M

2. 0.7M

3. 0.8M

4. 1.2M

For the reaction:

4NH₃(g) + 5O₂(g) → 4NO(g) + 6H₂O(l)

If 1 mol of NH₃ is mixed with 1 mol of O₂ and the reaction proceeds to completion, which of the following statements is correct?

1 g of magnesium is burnt with 0.56g of oxygen in a closed vessel. The left-out reactant and its quantity are:

(At. weight of Mg = 24, O=16)

What is the mole fraction of the solute in a 1.00 molal aqueous solution?

1. 32 g
2. 16 g
3. 8 g
4. 4 g

The molality of a 20% (by mass) CaCO₃ solution is : 
(Given: Density of solution is 1.2 gm/ml)

What is the ratio of the number of atoms in 2.2 g of CO₂ and in 1.7 g of NH₃?

An organic compound has the following composition by mass: C = 40.687%, H = 5.085%, O = 54.228%. Given vapour density = 59, find its molecular formula.

1. C₄H₆O₄

2. C₄H₆O₂

3. C₄H₄O₂

4. None of the above