Question

A neutral atom of beryllium (Be) has an average mass of 9 amu and 4 electrons. How many neutrons does it have?

Group of answer choices

4

9

13

5

Answer 1

To find the number of neutrons in a neutral atom of beryllium (Be), we can use the formula:

\[
\text{Number of neutrons} = \text{mass number} - \text{number of protons}
\]

The mass number is given as approximately 9 amu for beryllium. The atomic number of beryllium, which tells us the number of protons, is 4.

Substituting the values into the formula:

\[
\text{Number of neutrons} = 9 - 4 = 5
\]

Therefore, a neutral atom of beryllium has **5 neutrons**.

So the correct answer is:

**5**