The percentage composition of $H, C$,and $O$ in $H_2C_2O_4$ is respectively:

$A$ 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 $10.0 \ L$ of this welding gas (measured at $STP$) is found to weigh $11.6 \ g$. Calculate: $(i)$ Empirical formula,$(ii)$ Molar mass of the gas,$(iii)$ Molecular formula.

When a crystalline salt $Na_2SO_4 \cdot xH_2O$ is heated,it loses $55.9\%$ of its weight. What is the formula of the crystalline salt?

An organic compound containing $C$ and $H$ has $92.3 \%$ of carbon. Its empirical formula is:

The weight percentage of $C$ and $H$ in a hydrocarbon is in the ratio of $4: 1$. What is its empirical formula?

If the weight percentage of $Se$ (at. wt. $78.4$) in peroxidase anhydrous enzyme is $0.5 \%$,what is the minimum molecular weight of the enzyme?