Question

What is the mass number of the isotope lithium-7??

Answer 1

Explanation:

Mass number is the sum of total number of protons and total number of neutrons present in an atom.  

For example, a neutral atom of lithium has mass number 7 and atomic number 3.

Atomic number means the total number of protons present in an atom.

So, isotope of lithium-7 will have 3 protons and 4 neutrons. Thus, mass number of lithium-7 will be 3 + 4 = 7.

Answer 2

Lithium-7 is by far the most-common isotope, making up about 92.5 percent of all natural lithium. A lithium-7 atom contains three protons, four neutrons, and three electrons.