Which is an example of an atom?
a) the smallest unit of ne.
b) the smallest unit of p4.
c) the smallest unit of nh3.
d) the smallest unit of h2o.

Option A

Explanation:

An atom is the smallest particle of a chemical element that can exist.

Using the method of elimination;

Option A - This correct because an atom is the smallest unit of a chemical element ( Neon). It fits the definition given above.

Option B - This option is wrong  because P4 is a substance that is made up of four atoms of the same element, so it is a molecular element and not an atom.

A chemical compound is a chemical substance composed of many identical molecules composed of atoms from more than one element held together by chemical bonds.

Option C - This option is wrong because NH3 is a compound containing two different elements.

Option D - This option is wrong because H2O is a compound containing two different elements.