Crystals are substances with a regular, repeating arrangement of atoms. You can see this clearly in any image you get of any crystalline formation.
You can get this answer, either by knowledge or elimination. Some terms cannot even have atoms (atomic number, buffer, etc.), others aren't even substances (chemical bond, chemical reaction, covalent bond, pH) and yet others are so small atoms don't fit in them (proton, neutron).
Image description: Crystalline formation - differences with other formations.
Hope it helped,
BioTeacher101