Question

which are different forms of an element that have different numbers of neutrons?
ions
isotopes
compounds
molecules

Explanation:

• Ions: Atoms or molecules with a net electric charge due to loss or gain of electrons, not related to neutron number differences.
• Isotopes: Different forms of an element with the same number of protons but different numbers of neutrons.
• Compounds: Substances formed from two or more elements chemically combined, not about neutron - number variations within an element.
• Molecules: Groups of atoms bonded together, not relevant to neutron - number differences for an element.

Answer:

Isotopes.