When the first electron gain enthalpy $$\left( {{\Delta _{eg}}H} \right)$$ of oxygen is $$-$$ 141 kJ/mol, its second electron gain enthalpy is :

Aluminium is usually found in +3 oxidation state. In contrast, thallium exists in + 1 and + 3 oxidation states. This is due to :

In general, the properties that decrease and increase down a group in the periodic table, respectively, are :

The correct order of electron affinity is :