In Zn₃(PO₄)₂, the valency of Zn and Phosphate respectively is:

1. 3 and 2
2. 2 and 6
3. 4 and 6
4. 2 and 3

In Ca₃(PO₄)_x, the value of x is:

1. 1
2. 2
3. 3
4. 4

Which of the following represent the correct chemical formula of a compound :

1. NaSO₄
2. AlSO₄
3. NH₄PO₄
4. Ca₃N₂

A chemical equation is always balanced to satisfy the conditions of :

1. Law of constant proportions.

2. Gay Lussac's law

3. Law of conservation of mass

4. Law of mass action.