What is the difference between $\Delta H$ and $\Delta U$ for the combustion of methane at $25\,^oC$?

For the reaction $2 Cl ( g ) \rightarrow Cl _{2}( g )$,the correct option is

Two liters of $N_2$ gas at $0 \, ^\circ C$ and $5 \, atm$ pressure undergoes isothermal expansion against a constant external pressure of $1 \, atm$ until the pressure of the gas becomes $1 \, atm$. If the gas is ideal,what is the work done in the expansion in $J$?

The enthalpy change on freezing of $1 \ mol$ of water at $5 \ ^\circ C$ to ice at $-5 \ ^\circ C$ is ..... $kJ \ mol^{-1}$.
(Given $\Delta _{fus}H = 6 \ kJ \ mol^{-1}$ at $0 \ ^\circ C$,
$C_p(H_2O, l) = 75.3 \ J \ mol^{-1} \ K^{-1}$,
$C_p(H_2O, s) = 36.8 \ J \ mol^{-1} \ K^{-1}$)

How much energy in $kJ$ is required to convert $54 \ g$ of ice at $0 \ ^\circ C$ to water at $27 \ ^\circ C$? $\left( \Delta H_{fusion} = 6.01 \ kJ \ mol^{-1}, C_{p(liquid)} = 4.18 \ J \ K^{-1} \ g^{-1} \right)$

The enthalpies of formation of gaseous $N_2O$ and $NO$ at $298 \ K$ are $82.0$ and $90.0 \ kJ \ mol^{-1}$ respectively. The enthalpy change of the reaction $N_2O_{(g)} + \frac{1}{2} O_{2(g)} \rightarrow 2 NO_{(g)}$ is