$20$ carat gold contains ...... $(\%)$ percent gold.

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 .......

Calculate the mass percent of calcium,phosphorus,and oxygen in calcium phosphate $Ca_{3}(PO_{4})_{2}$.

$A$ hydrocarbon contains $75\%$ carbon by mass. What is its empirical formula?

$A$ compound contains $75.8\%$ of $X$ and $24.2\%$ of $Y$ by mass. If the atomic weights of $X$ and $Y$ are $24$ and $16$ respectively,find the empirical formula of the compound.

An organic compound has the percentage of $C$ and $H$ in the ratio $6 : 1$ and the percentage of $C$ and $O$ in the ratio $3 : 4$. The compound is: