The compound which contains both ionic and covalent bond:

Explanation

Option B is correct.The compound that contains both ionic and covalent bonds is KCN. In KCN, the potassium (K) atom is a metal and the nitrogen (N) atom is a nonmetal. The electronegativity difference between potassium and nitrogen is 2.1, which is considered to be a large difference. This means that the bond between potassium and nitrogen is mostly ionic. However, the nitrogen atom in KCN also has a lone pair of electrons. This lone pair of electrons can be donated to the potassium atom to form a coordinate covalent bond. A coordinate covalent bond is a covalent bond in which one atom donates both of the shared electrons.