the answer is C
Explanation:
A chemical change involves changing a sustance(s) into a different substance(s).
In (a), all you are doing is physically mixing two compounds. The compounds do not change their identities. You can separate them from each other if you want to by physical means (dissolution, filtering, etc.).
In (b), assuming that the mixture consists of only the two elements, nothing has changed its identity.
In (d), changing from a solid to liquid is simply melting. If I melt an ice cube, solid H2O, into a liquid, the substance is still H2O.
In (c), to separate a compound into two elements, I have to break chemical bonds. Example:
2HgO(s) ==> 2Hg(l) + O2(g)
If I heat mercury(II) oxide, it will decompose into metallic Hg and oxygen gas. The substance changed its identity from HgO to Hg + O2.
A,C, is a chemical change as new substance is formed in these reactions and the reaction is not easily reversed
in B a mixture can formed again by mixing the two elemenets
in d the liquid can again turn to solid
b and d is a physical change
