Nickel steel contains $3-5 \%$ of $Ni$. (in $-5 \%$)

Calculate the mass percent of different elements present in sodium sulphate $(Na_{2}SO_{4})$.

The percentage composition of an organic compound is as follows: $C = 10.06\%$,$H = 0.84\%$,$Cl = 89.10\%$. Which of the following corresponds to its molecular formula if the vapour density is $60.0$?

$A$ welding fuel gas contains carbon and hydrogen only. Burning a small sample of it in oxygen gives $3.38 \, g$ of carbon dioxide,$0.690 \, g$ of water,and no other products. $A$ volume of $10.0 \, L$ (measured at $STP$) of this welding gas is found to weigh $11.6 \, g$. Calculate:
$(i)$ empirical formula,
$(ii)$ molar mass of the gas,and
$(iii)$ molecular formula.

An organic compound contains $C = 40\%$,$H = 13.33\%$,and $N = 46.67\%$. Its empirical formula is:

An organic compound made of $C$, $H$ and $N$ contains $20 \%$ nitrogen. Its molecular weight is: