GC Atomic Structure

Two atoms are said to be isotopes if

  1. they have the same atomic number but different mass numbers
  2. the sum of the number of protons and neutrons is the same, but the number of protons is different
  3. they have the same number of neutrons but different modes of radioactive decay
  4. they have the same number of neutrons but different mass numbers

Answer

The correct option is A.