$NH_2^-$,$NH_3$ and $NH_4^+$ do not show similarity in the following:

Observe the following statements:
$i$. The dipole moment of $NH_3$ is higher than the dipole moment of $NF_3$.
$ii$. The dipole moment of chloroform $(CHCl_3)$ is zero.
$iii$. Covalent bond character in $NaCl$ is more compared to $CuCl$.

The decreasing order of $C-C$ bond length is:
$I.$ $C_2H_4$ $II.$ $C_2H_2$
$III.$ $C_6H_6$ $IV.$ $C_2H_6$

Which of the following statements is incorrect?

The ratio of $\sigma$-bond and $\pi$-bond in tetracyanoethylene is

The compound in which the number of $d\pi - p\pi$ bonds are equal to those present in $ClO_4^{-}$ is: