Question

protons and isotopes quick check
beryllium has an atomic number of 4. how many neutrons does the isotope beryllium - 9 have? (1 point)
13
9
5
4

Explanation:

Step1: Recall atomic - mass formula

Atomic mass = number of protons+number of neutrons.

Step2: Identify number of protons

The atomic number is equal to the number of protons. Beryllium has an atomic number of 4, so the number of protons is 4.

Step3: Determine atomic mass of beryllium - 9

The isotope is beryllium - 9, so the atomic mass is 9.

Step4: Calculate number of neutrons

Let the number of neutrons be $n$. We have $9 = 4 + n$. Solving for $n$, we get $n=9 - 4=5$.

Answer:

C. 5