The oxygen molecule is paramagnetic due to

Which of the following species are hypervalent?

$1$. ${\mathrm{ClO}}_4^{-}$

$2$. ${\mathrm{BF}}_3$

$3$. ${\mathrm{SO}}_4^{2-}$

$4$. ${\mathrm{CO}}_3^{2-}$

The total number of covalent bonds formed in the Lewis structures of given species respectively are:

(a) ${\mathrm{CO}}_3^{2-}$

(b) ${\mathrm{CCl}}_4$

(c) ${\mathrm{NF}}_3$

(d) ${\mathrm{HNO}}_3$