Question

____ are different forms of a single element.
a atoms
b elements
c ions
d isotopes

Explanation:

To solve this, we analyze each option:

• Option A: Atoms are the basic units of matter, but the term for different forms of a single element with same protons but different neutrons is not just "atoms".
• Option B: Elements are pure substances, not different forms of a single element (they are distinct substances).
• Option C: Ions are charged atoms, related to electron gain/loss, not about different forms of an element due to neutrons.
• Option D: Isotopes are defined as atoms of the same element with the same number of protons but different numbers of neutrons, so they are different forms of a single element.

Answer:

D. Isotopes