Question

a neutral atom has 53 protons and 74 neutrons. what is its mass number?
127
121
74
53

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 values

Given $p = 53$ and $n=74$. Then $A=53 + 74$.

Step3: Calculate the result

$53+74 = 127$.

Answer:

A. 127