Two more substances put together but each retaining their own identity is a

The answer is Mixture.  Two more substances put together but each retaining their own identity is a Mixture.  They are two or more substances dispersed in one another but each retaining their own identity.

Most likely a is the answer - because  you generate   38 atp's but also consume an atp.   each atp gives approx. less than 4 kcal so probably a is the closest answer.

Less stable  hope this