20.0 g of a magnesium carbonate sample decomposes on heating to give carbon dioxide and 8.0 g of magnesium oxide.
The percentage purity of magnesium carbonate in the sample will be: 
(Atomic weight of Mg=24)

10 g of hydrogen and 64 of oxygen were filled in a steel vessel and exploded. The amount of water produced in this reaction will be:

1. 2 mol

2. 3 mol

3. 4 mol

4. 1 mol

The moles of lead (II) chloride that will be formed from a reaction
between 6.5 g of PbO and 3.2 g of HCl are:

1. 0.044
2. 0.333
3. 0.011
4. 0.029