Plz if you !
a and c are compounds. substance d is an element.
b and d are compounds. a and c are elements.
b is a compound, a, c and d are all elements
a and c are elements. substance d is a compound.

The answer to your question is: A and C are elements. Substance D is a compound.

Explanation:

We know that A and C cannot be broken down into anything simpler then we conclude  that they are elements.

Also know that B is composed by A and D and are not chemically bonded, so we conclude that B is a mixture

Finally, D can be decomposed into A and C, so it's a compound.

The only possible answer is the last one.

b.final

the number of protons in the nucleus of a given element. has slight luster and conducts electricity at high temperatures like metal.but like a nonmetal,boron is brittle and does not conduct electricity well at low temperatures. in graphite, carbon is a soft,brittle solid.it is reflective,ductile,or malleable.