${\mathrm{SO}}_2$ required for industrial production of sulphuric acid is produced by burning iron pyrites in excess air current. The chemical equation of the current is given below:

 

$4{\mathrm{FeS}}_2 + 11{\mathrm{O}}_2 \to 2{\mathrm{Fe}}_2{\mathrm{O}}_3 + 8{\mathrm{SO}}_2$

How many grams of ${\mathrm{FeS}}_2$ is required for the production of $512\mathrm{g}$ of ${\mathrm{SO}}_2$? $\left[\mathrm{Fe}=56, \mathrm{S}=32, \mathrm{O}=16\right]$

By heating $32.1 \mathrm{g}$ ammonium chloride with calcium hydroxide $10.2 \mathrm{g} {\mathrm{NH}}_3$ , $33.3 \mathrm{g} {\mathrm{CaCl}}_3$  and $10.8 \mathrm{g} {\mathrm{H}}_2\mathrm{O}$ are obtained. How many grams of calcium hydroxide take part in the reaction? How many moles of ${\mathrm{NH}}_3$ and how many litres of ${\mathrm{NH}}_3$, at STP is formed at the reaction? 

According to the following chemical equation,

${\mathrm{CH}}_4+2{\mathrm{O}}_2\to {\mathrm{CO}}_2+2{\mathrm{H}}_2\mathrm{O}$

what volume of ${\mathrm{O}}_2$ will be required to burn $10$ mole of ${\mathrm{CH}}_4$ at STP?

A and B react to produce C according to the following chemical equation 
$2\mathrm{A} + \mathrm{B} \to 2\mathrm{C}$

A, B and C are the formulas for three gaseous substances. The vapour densities of A and B are 32 and 16 respectively. Find out the vapour density of C.