Answer:
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.
