In which of the following set of molecules the hybridisation of central atoms is different?

At 300 K and 760 torr pressure, the density of a mixture of He and $\mathrm{O}_2$ gases is $0.543 \mathrm{gL}^{-1}$. The mass percent of oxygen approximately is $$ \left(R=0.0821 \mathrm{~L} \mathrm{~atm} \mathrm{~K}^{-1} \mathrm{~mol}^{-1}\right) $$

The equivalent weight of which of the following is maximum? (Given : atomic weights $\mathrm{Na}=23, \mathrm{Mn}=55$, $$ \mathrm{Cr}=52, \mathrm{~K}=39, \mathrm{O}=16, \mathrm{C}=12) $$

If 2.5 moles of an ideal gas at a certain temperature are allowed to expand isothermally and reversibly from an initial volume of $2 \mathrm{dm}^3$ to $20 \mathrm{dm}^3$, the work done by the gas is -16.5 kJ . The temperature (in K ) of the gas is (Round off to the nearest value) ( $R=8.314 \mathrm{~J} \mathrm{~K}^{-1} \mathrm{~mol}^{-1}$ )