Question

question 15: an atom of beryllium has 4 protons, 4 electrons, and 5 neutrons. what is the mass number of this atom? a 4 b 5 c 9 d 13

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: Identify number of protons and neutrons

Given that the beryllium atom has $p = 4$ protons and $n=5$ neutrons.

Step3: Calculate mass number

Substitute the values into the formula: $A=4 + 5=9$.

Answer:

C. 9