23. what is the mass number of a cobalt atom that has 27 protons and 30 neutrons?\na 62\nb 34\nc 57\nd 49

Answer:

C. 57

Explanation:

Step1: Recall mass - number formula

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

Step2: Substitute given values

Given $p = 27$ and $n=30$. Then $A=27 + 30$.

Step3: Calculate the result

$27+30 = 57$.