Answer:
Compound.
Explanation:
A compound is a substance formed when two or more elements are chemically joined. Water, salt, and sugar are examples of compounds. When the elements are joined, the atoms lose their individual properties and have different properties from the elements they are composed of.
Explanation:
Given that,
(a) Frequency, 
All electromagnetic wave moves with the speed of light. It is given by :


(b) Frequency, 
All electromagnetic wave moves with the speed of light. It is given by :


Hence, this is the required solution.
The answer is D. When you melt something, it only changes its physical change.