Set – A	Set – B
A) Co-ordinate covalent – bond	1) ${\text{NH}}_4\text{C}l$
B) Covalent bond	2) ${\text{H}}_3{\text{O}}^{+}$
C) Molecule having ionic, covalent, Dative bonds	3) ${\text{O}}_2$

A) ${\text{H}}_3{\text{O}}^{+}$ formed by combining ${\text{H}}^{\text{+}}{\text{ and H}}_{\text{2}}\text{O}$,  ${\text{H}}_{\text{2}}\text{O}$ donate a pair of electrons and act as donor, ${\text{H}}^{+}$ ion accept a pair of electrons and act as acceptor and hence co-ordinate covalent bond is formed. ( ${\text{H}}_3{\text{O}}^{+}$is ionic in nature.

B) Oxygen atoms can each form two (double) covalent bonds. Two pairs of electrons are shared in an oxygen molecule $\left(O_2\right)$so they formed a double bond.

C) ${\text{NH}}_4\text{C}l$Contains ionic bond between ${\text{NH}}_{\text{4}}^{\text{+}}$ and $\text{C}{l}^{-}$, in ${\text{NH}}_{\text{4}}^{\text{+}}$ covalent bonds are present between nitrogen and hydrogen’s, between ${\text{NH}}_3{\text{ and H}}^{\text{+}}$  dative bond is formed here nitrogen donate pair of electrons to ${\text{H}}^{\text{+}}$.