Question

what is the mass number for an atom of xenon containing 54 protons and 77 neutrons?

Explanation:

Step1: Recall mass - number formula

The mass number (A) of an atom is the sum of the number of protons (p) and neutrons (n). The formula is $A=p + n$.

Step2: Substitute given values

Given $p = 54$ and $n=77$. Then $A=54 + 77$.

Step3: Calculate the sum

$54+77 = 131$.

Answer:

131