Bond enthalpies of $$A_2, B_2$$ and $$A B$$ are in the ratio $$2: 1: 2$$. If bond enthalpy of formation of $$A B$$ is $$-100 \mathrm{~kJ} \mathrm{~mol}^{-1}$$. The bond enthalpy of $$B_2$$ is

Bond angle is $$\mathrm{PH}_4^{+}$$ is more than that of $$\mathrm{PH}_3$$. This is because

Incorrectly matched pair is

Which of the following has the lowest boiling point?