Which statement most accurately describes the second law of thermodynamics?

a. energy cannot be changed from one form to another without a loss of usable energy
b. one usable form of energy can be completely converted into another usable form.
c. energy cannot be created nor destroyed but it can be changed from one form to another.
d. energy cannot be created or destroyed.
e. energy cannot be transformed.

Energy cannot be changed from one form to another without a loss of usable energy

Explanation:

Second law of thermodynamics states that the total entropy or the randomness of the system remains constant over time.  It also states that the net entropy will remain the same or it will increase.

Entropy of a system is given by heat absorbed divided by temperature. It is given by :

So, the correct option is (A) "Energy cannot be changed from one form to another without a loss of usable energy".