Question

select the correct answer.
which option describes a similarity and a difference between isotopes of an element?
a. same atomic number; different number of protons
b. same number of protons; different atomic number
c. same atomic number; different mass number
d. same mass number; different atomic number
e. same number of neutrons; same number of protons

Explanation:

Isotopes of an element have the same atomic number (which equals the number of protons) but different mass numbers (since mass number = protons + neutrons, and isotopes differ in neutrons). Option A is wrong as protons are same. Option B is wrong (atomic number same). Option D is wrong (mass number differs). Option E is wrong (neutrons differ). So C is correct.

Answer:

C. same atomic number; different mass number