In the above reaction,$3.9 \ g$ of benzene on nitration gives $4.92 \ g$ of nitrobenzene. The percentage yield of nitrobenzene in the above reaction is............. $\%$. (Round off to the Nearest Integer).
(Given atomic mass: $C : 12.0 \ u$,$H : 1.0 \ u$,$O : 16.0 \ u$,$N : 14.0 \ u$)

Molarity of a given orthophosphoric acid solution is $3 \ M$. Its normality is (in $N$)

$A$ $6 \ L$ sample of hard water has a total hardness of $200 \ ppm$ of $Mg^{2+}$ in the form of bicarbonates and chlorides. This sample is treated with $Na_2CO_3$ to eliminate all temporary hardness,and the new hardness is found to be $\frac{1000}{3} \ ppm$ of $CaCO_3$. Find the mass of $MgCl_2$ in the $6 \ L$ sample in $mg$. $(d_{H_2O} = 1 \ g/mL)$

$1.84 \ g$ of a mixture of $CaCO_3$ and $MgCO_3$ is strongly heated to get a residue of $0.96 \ g$. The percentage of $CaCO_3$ in the mixture is

$A$ pre-weighed vessel was filled with oxygen at $N.T.P.$ and weighed. It was then evacuated,filled with $SO_2$ at the same temperature and pressure,and again weighed. The weight of oxygen will be

$10 \ mL$ of $1 \ M$ $H_2SO_4$ will completely neutralize: