the element radium has a mass number of 226 and an atomic number of 88. how many neutrons does an atom of…

Explanation:

Step1: Recall the formula

The mass number ($A$) is the sum of protons and neutrons, and the atomic number ($Z$) is the number of protons. The formula for calculating the number of neutrons ($N$) is $N = A - Z$.

Step2: Substitute values

Given $A = 226$ and $Z = 88$, then $N=226 - 88$.

Step3: Calculate result

$226-88 = 138$.

Answer:

C. 138