In which of the following changes there is no change in hybridisation of the central atom?

The rate of diffusion of a gas $A$ is $\sqrt{5}$ times more than that of gas $B$. If the molar mass of $A$ is $x \mathrm{~g} \mathrm{~mol}^{-1}$, the molar mass of $B$ (in $\mathrm{g} \mathrm{mol}^{-1}$ ) is

Which one of the following has the same number of atoms as are in 6 g of $\mathrm{H}_2 \mathrm{O}$ ?

For the reaction at $25^{\circ} \mathrm{C}, X_2 \mathrm{O}_4(l) \longrightarrow 2 \mathrm{XO}_2(g), \Delta U$ and $\Delta S$ are 2.1 k cal and $20 \mathrm{cal} / \mathrm{K}$ respectively. What is $\Delta \mathrm{G}$ for the reaction at the same temperature? ( $R=2 \mathrm{cal} \mathrm{K}^{-1} \mathrm{~mol}^{-1}$ )