Boron has two isotopes, boron-10 and boron-11. Boron-10 has five protons and five neutrons. How many protons and neutrons does boron-11 have? Explain.
Five protons and six neutrons.
We are given that boron-10 had five protons in its nucleus, and any element always has the same number of protons in its nucleus (atomic number). So boron-11 has five protons the same as boron-10.
Then the mass number is total protons plus neutrons. For boron-11 this total is 11, and five of the particles are protons, thus