What is the smallest possible piece that an element can be broken down into by normal laboratory processes?
a. atom
b. mixture
c. solution
d. compound

a. Atom

Explanation:

Atom is the fundamental and smallest unit of matter which contains electrons, protons and neutrons. It cannot be decomposed into simpler constituents using chemical reactions.

Mixture is a substance which has two or more components which do not combine chemically and do not have any fixed ratio in which they are present. Example: Air. It can be decomposed into simpler constituents using physical reactions.

Solution is a homogeneous mixture of a solute and a solvent. Example: salt in water. It can be decomposed into simpler constituents using physical reactions.

Compound is a pure substance which is made from atoms of different elements combined together in a fixed ratio by mass. Example: water . It can be decomposed into simpler constituents using chemical reactions.