Among the given all compounds ${\mathrm{COCl}}_2$is a true covalent. Because in this compound all elements are non metallic only. But in the remaining three compounds one atom is a metal and the other one is non metal. Hence the electrovalent bond or ionic bond is formed between the atoms.

$\mathrm{EX};\mathrm{AgCl},\mathrm{Kcl},{\mathrm{BaCl}}_2$