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? ( $R=2 \mathrm{cal} \mathrm{K}^{-1} \mathrm{~mol}^{-1}$ )

Which of the following does not form a buffer solution?

The hydrides of which group elements of the periodic table form electron precise hydrides?