Answer:
4. H-3 and He-4
Explanation:
H-3 means hydrogen with a mass number of 3. Mass number is the addition of protons and neutrons in the nucleus. Hydrogen always has 1 proton because it has atomic number 1, therefore the number of neutrons is found by subtracting 1 from the mass number (3).
3-1= 2 neutrons
He-4 also has 2 neutrons. He-4 has mass number 4, which means that its protons and neutrons added together equals 4. Helium has 2 protons because it has atomic number 2.
Therefore 2 + neutrons =4
neutrons =4-2
neutrons =2
