Pick out the isoelectronic structures from the following
I. $$CH_3^+$$
II. $$H_3O^+$$
III. $$NH_3$$
IV. $$CH_3^-$$

The maximum number of hydrogen bonds a water molecule can form is

The cyanide ion, CN^- and N₂ are isoelectronic, But in contrast to CN^-, N₂ is chemically inert, because of

The type of hybrid orbitals used by the chlorine atom in $$ClO_2^-$$ is