The covalency of nitrogen in ${\mathrm{HNO}}_3$ is:

Which of the following species are hypervalent?

$1$. ${\mathrm{ClO}}_4^{-}$

$2$. ${\mathrm{BF}}_3$

$3$. ${\mathrm{SO}}_4^{2-}$

$4$. ${\mathrm{CO}}_3^{2-}$

Which among the following resonance structures of ${{\mathrm{N}}_3}^{-}$ satisfies the octet rule but is ruled out as resonance structure?