The stability of +1 oxidation state among Al, Ga, In and Tl increases in the sequence

The variation of the boiling points of the hydrogen halides is in the order HF > HI > HBr > HCl.

What explains the higher boiling point of hydrogen fluoride?

Strong reducing behavior of H₃PO₂ is due to

The formation of the oxide ion, O^2$$-$$_(g) from oxygen atom requires first an exthermic and then an endothermic step as shown below:
O_(g) + e^$$-$$ $$ \to $$ O^$$-$$_(g);  $$\Delta $$_fH^o = $$-$$141 kJ mol^$$-$$1

O^$$-$$_(g) + e^$$-$$ $$ \to $$ O^2$$-$$_(g);  $$\Delta $$_fH^o = +780 kJ mol^$$-$$1

Thus, process of formation of O^2$$-$$ is isoelectronic with neon. It is due to the fact that,