(iii) While aluminium has an empty d-orbital to accommodate the electrons from the fluorine atom, boron does not have an empty d-orbital.
(iv); Pb is a part of the periodic table’s group 14. (carbon family). This element’s valence shell electronic configuration is ns2 np2. The oxidation states of Pb can vary between +2 and +4.
Due to the inert pair effect, the lower oxidation state, i.e. +2, is more stable than the higher one when travelling from top to bottom in the group.
As a result of the inert pair effect (poor shielding of the inner electronic orbitals), Pb displays +2 rather than +4 as a stable oxidation state.