H₃PO₄ is a tribasic acid and one of its salts is NaH₂PO₄. What volume of 1 M NaOH should be added to 12g NaH₂PO₄ (Molar mass 120) to exactly convert it into Na₃PO₄?

(a) 100 mL

(b) 300mL

(c) 200mL

(d) 80mL

A metal M forms a compound M₂HPO₄. The formula of the metal sulphate is:

(a) M₂SO₄ 

(b) MSO₄

(c) M(SO₄${)}_2$

(d) M₂(SO₄)₃

One mole of a mixture of CO and CO₂ requires exactly 20g of NaOH in solution for complete conversion of all the CO₂ into Na₂CO₃. How much NaOH would it require for conversion into Na₂CO₃, if the mixture (one mole) is completely oxidised to CO₂?

(a) 60g

(b) 80g

(c) 40g

(d) 20g

The oxide of a metal contains

40% by mass of oxygen. The percentage of chlorine in the chloride of the metal is

1) 84.7

(2) 74.7

(3) 64.7

(4) 44.7

Copper forms two oxides. For the same amount of copper, twice as much oxygen was used to form first oxide than to form second one. What is the ratio of the valencies of copper in first and second oxides?

1. 2:5

2. 1:6

3. 2:1

4. 1:2