The ionic charges on chromate ion and dichromate ion respectively is

In the reaction, $\mathrm{C}_6 \mathrm{H}_5 \mathrm{COCH}_3 \xrightarrow[\mathrm{Zn}-\mathrm{Hg} / \text { conc. } \mathrm{HCl}]{[\mathrm{H}]} X,X$ is

What is the percentage of carbon in urea? (Atomic mass $C=12, H=1, N=14, O=16$)

$\alpha$ - butylene when subjected to hydroboration oxidation reaction, yields