Two atoms with the same number of protons but a different number of neutrons are a. ions of the same element. b. in the same column of the periodic table. c. next to each other on the periodic table. d. isotopes of the same element.

option D. isotopes of the same element.

Explanation:

1) The number of protons is the atomic number of the element. Atomic number is what identifies the element. None two different elements can have the same atomic number (number of protons).

On the other hand, the atoms of an element can differ on the number of neutrons.

Isotopes are atoms of the same element, ergo with the same number of protons, but different number of neutrons.

As per the other choices:

A) ions are charged particles: substances with either excess or defect of electrons.

B) There are several different elements (kind of atoms) in a column of the periodic table, and, of course, being different elements they have different number of protons

C) Two atoms next to each other on the periodic table are different kind of atoms, so they have different number of protons.

it is b that is the answer.