Which of the following combinations illustrates the law of reciprocal proportions?

1.  ${\mathrm{N}}_2{\mathrm{O}}_3, {\mathrm{N}}_2{\mathrm{O}}_4, {\mathrm{N}}_2{\mathrm{O}}_5$

2.  $\mathrm{NaCl}, \mathrm{NaBr}, \mathrm{Nal}$

3.  ${\mathrm{CS}}_2, {\mathrm{CO}}_2, {\mathrm{SO}}_2$

4.  ${\mathrm{PH}}_3, {\mathrm{P}}_2{\mathrm{O}}_3, {\mathrm{P}}_2{\mathrm{O}}_5$

The formula of an acid is ${\mathrm{HXO}}_2.$ The mass of 0.0242 moles of the acid is 1.657 g.
The atomic weight of X is:

The sulphate of the metal M contains 9.87% of M. This sulphate is isomorphous with ${\mathrm{ZnSO}}_4.7{\mathrm{H}}_2\mathrm{O}$. The atomic weight of M is:

1.  40.3

2.  36.3

3.  24.3

4.  11.3

Sulphur burns according to the reaction

 $\frac{1}{8}{\mathrm{S}}_8\left(\mathrm{s}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)$ $\stackrel{}{\to }$ ${\mathrm{SO}}_2\left(\mathrm{g}\right)$
What volume of air, at 1 atm and 273 K, containing 21%  oxygen by volume is required to completely burn sulphur $\left({\mathrm{S}}_8\right)$ present in 200 g of the sample?
(This sample contains 20% inert material which does not burn)

1.  23.52 litre

2.  320 litre

3.  112 litre

4.  533.33 litre

100 mL of ${\mathrm{H}}_2{\mathrm{SO}}_4$ solution having molarity of 1M and density 1.5 g/mL is mixed with 400 mL of water. The molarity of the ${\mathrm{H}}_2{\mathrm{SO}}_4$ solution will be: (final density is 1.25 g/mL )

Which of the following is dependent on temperature?

A mixture of 2.3 g formic acid and 4.5 g oxalic acid is treated with conc. ${\mathrm{H}}_2{\mathrm{SO}}_4$. The evolved gaseous mixture is passed through KOH pellets.

Weight (in g) of the remaining product at STP will be:

1. 1.4

2. 3.0

3. 2.8

4. 4.4

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 is: 
(Atomic weight of Mg=24)