The percentage of $N_2$ in urea is about

The empirical formula of a compound is $CH$. Its molecular weight is $78$. The molecular formula of the compound will be

An organic compound was found to contain $40.0 \% C$ and $6.66 \% H$. Find its molecular formula (molar mass $= 180$).

The molecular formula of potash alum is

Arrange the following compounds in the increasing order of percentage of chlorine by weight:
$I.$ $DDT$ $(C_{14}H_9Cl_5)$
$II.$ Gammaxene $(C_6H_6Cl_6)$
$III.$ Carbon tetrachloride $(CCl_4)$
$IV.$ Chlorobenzene $(C_6H_5Cl)$

An organic compound having molecular mass $60$ is found to contain $C = 20\%$,$H = 6.67\%$,and $N = 46.67\%$,while the rest is oxygen. On heating,it gives $NH_3$ along with a solid residue. The solid residue gives a violet color with alkaline copper sulphate solution. The compound is: