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

Mass percentage of $C, H$ and $O$ in a compound are $60\%$,$13.33\%$ and $26.67\%$ respectively. The molecular weight of the compound is $60$. The molecular formula of the compound is

An oxide of iron,which contains $69.9 \%$ iron and $30.1 \%$ dioxygen by mass,has the empirical formula:

Hemoglobin contains $0.34 \%$ of iron by mass. The number of $Fe$ atoms in $3.3 \ g$ of hemoglobin is. (Given : Atomic mass of $Fe$ is $56 \ u, N_A = 6.022 \times 10^{23} \ mol^{-1}$)

In a substance,the number of atoms of $Cr$ and $O$ are $4.8 \times 10^{10}$ and $9.6 \times 10^{10}$ respectively. The empirical formula of the substance is .......

The molecular formula of the chloride of a metal $M$ is $MCl_3$. The formula of its carbonate would be: