Question

An atom contains 3 protons, 3 electrons and 4 neutrons. Find its atomic number, mass number and valency?

Answer 1

A lithium atom contains 3 protons in its nucleus irrespective of the number of neutrons or electrons. Notice that because the lithium atom always has 3 protons, the atomic number for lithium is always 3. The mass number, however, is 6 in the isotope with 3 neutrons, and 7 in the isotope with 4 neutrons