A) BaSO4+ZnS (lithopone) is a brilliant white pigment used in water-based paints. It is a mixture of BaSO4 and ZnS
B) NI3
Nitrogen triiodide . It is an extremely sensitive contact explosive: small quantities explode with a loud, sharp snap when touched even lightly.
C) N2O4
Dinitrogen tetroxide is a powerful oxidizer that is hypergolic (spontaneously reacts) upon contact with various forms of hydrazine, which makes the pair a popular bipropellant for rockets.
D) KO2 is used as space capsule.
Hence answer is A 4, B 1, C 2, D 3