Question

Which of these pairs of atoms are isotopes?

1. Atom A: 13 protons, 12 neutrons and 12 electrons. Atom B: 12 protons, 12 neutrons and 12 electrons
2. Atom A: 12 protons, 12 neutrons and 12 electrons. Atom B: 12 protons, 12 neutrons and 13 electrons
3. Atom A: 12 protons, 12 neutrons and 12 electrons. Atom B: 12 protons, 13 neutrons and 12 electrons

Answer 1

number 3

Step-by-step explanation:

In isotopes the number of protons and electrons is always the same since they are isotopes of the same element. If the number of protons in atom "a" is different than in atom "b" then these are 2 different elements.

Isotopes have the same number of electrons and protons but a different number if neutrons.