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: Recall the definition of mass number

The mass number of an isotope is given by the number in its name. For lithium - 7, the mass number is 7.

Step2: Use the formula for mass number

The mass number \(A\) of an atom is given by \(A = p + n\), where \(p\) is the number of protons and \(n\) is the number of neutrons.
For lithium - 8, \(A = 8\) and \(p=3\).
We can solve for \(n\) using the formula \(n=A - p\).
Substitute \(A = 8\) and \(p = 3\) into the formula: \(n=8 - 3\).

Step3: Calculate the number of neutrons

\(n=8 - 3=5\)

Answer:

7
5