Question

what is the mass number of the isotope lithium - 7?
lithium has 3 protons. how many neutrons are in the isotope lithium - 8?

Explanation:

Step1: Determine the mass number of lithium - 7

The mass number is given in the isotope name. For lithium - 7, the mass number is 7.

Step2: Calculate the number of neutrons in lithium - 8

The formula for the mass number \(A\) is \(A=\text{number of protons}(p)+\text{number of neutrons}(n)\). Given \(A = 8\) (from lithium - 8) and \(p=3\) (lithium has 3 protons). Rearranging the formula for \(n\), we get \(n=A - p\). Substituting the values: \(n=8 - 3\).

Answer:

7
5