Question

all atoms of the element sodium have 11 protons. how many neutrons are in an atom of sodium - 23?

a 28
b 23
c 12
d 11

Explanation:

Step1: Recall the formula for mass number

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 the values of $A$ and $p$

For sodium - 23, the mass number $A = 23$. Given that the number of protons $p=11$ (since all sodium atoms have 11 protons).

Step3: Solve for $n$

Rearrange the formula $n=A - p$. Substitute $A = 23$ and $p = 11$ into the formula: $n=23-11$.
$$n = 12$$

Answer:

C. 12