$A$ substance contains $38.8\%$ carbon,$16\%$ hydrogen,and $45.2\%$ nitrogen. What is the empirical formula of this substance?

$A$ metal oxide $M$ contains $40\%$ oxygen by mass. The atomic mass of metal $M$ is $24$. The empirical formula of the oxide is....

Complete combustion of $X$ g of an organic compound gave $0.25$ g of $CO_2$ and $0.12$ g of $H_2O$. If the percentage of carbon is $25\%$ and of hydrogen is $4.89\%$, then $X = \_\_\_\_ \times 10^{-3}$ g. (Nearest integer) (Molar mass of $C$, $H$ and $O$ are $12, 1$ and $16$ g mol$^{-1}$ respectively.)

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

If a compound contains $C = 18.5\%$,$H = 1.55\%$,$Cl = 55.04\%$,and $O = 24.81\%$,then its empirical formula is .....

The correct sequence in decreasing order of the percentage of nitrogen in the given compounds is