Arock can be broken down into different kinds of substances by physical processes. no chemical reactions are needed to separate different parts of a rock into pure substances. this is because a rock is a(n) .

I believe the correct answer is a mixture. Most rocks are just different compounds or elements somewhat fused through heat and pressure. The substances are not chemically bonded together which means that they all retain their chemical identity and therefore can be separated by breaking them up. A good example of this is granite where you can see the different compounds that got fused together and can falls apart when you grind it. I hope this helps. Let me know if anything is unclear.

A.(nh4)(2co3)is the correct answer