The normality of $1 \ M$ solution of $H_3PO_4$ will be.....$N$

Calculate the amount of water $(g)$ produced by the combustion of $16 \ g$ of methane. (in $g$)

What is the volume (in litres) of oxygen at $STP$ required for complete combustion of $32 \,g$ of $CH_4$? (Molecular weight of $CH_4$ is $16$)

$8 \ g$ of $CH_4$ is completely burnt in air. The number of moles of water produced are $.....$

What volume of ammonia is required to react with $250 \ mL$ of oxygen by following the reaction at same conditions?
$4NH_3(g) + 5O_2(g) \to 4NO(g) + 6H_2O(g)$

The formula of a metallic oxide is $MO$. What will be the formula of its phosphate?