Answer: Option (B) is the correct answer.
Step-by-step explanation:
An element is defined as a substance that contains same type of atoms.
For example, element K contains only atoms of potassium.
Whereas a substance in which two or more different elements chemically combine together in a fixed ratio by mass is known as a compound.
For example, KCl contains atoms of K and Cl in 1 : 1 ratio. Hence, it is a compound.
Therefore, in the chemical reaction,
there are only two elements which are K and Cl.