Two atoms with different mass number but the same atomic number are called a) elements. b) ions. c) isotopes. d) nuclei.

What you are describing is a difference in the nucleus of neutrons.

Elements: these chemicals are what is on the periodic table.

ions: These have either too many electrons or too few electrons from the elements found on the periodic table.

Nuclei: are the part of the atom found at the center.

The three above are NOT the answer.

The answer is C

are there answer choices to this question? this seems like a question where you have options to choose from.

layers of the earth affect the waves and these effects are seen on instruiments such as seimometers