Correct order of size is $\mathrm{Mg}>\mathrm{Al}>\mathrm{Mg}^{2+}>\mathrm{Al}^{3+}\\$ Atomic size depends mainly upon $\mathrm{Z}_{\text {effective }}$ and shell number. $\\$Generally on moving down the group electron affinity decreases and on moving across the period electron affinity increase. $\\$In the periodic table Cl has maximum electron affinity. Halogen has higher electron affinity than Chalcogen. $\\ \mathrm{Cl}>\mathrm{Br}>\mathrm{S}>\mathrm{O}$