An atom has a mass number of 9 and 5 neutrons. What is its atomic number? A 19 B. 14 O c.4 D. 11 SN

Explanation:

First, define some important terms.

We know the mass number is 9. So, the sum of protons and neutrons is 9.

We also know the atoms has 5 neutrons. Therefore, the rest must be protons.

Subtract the 5 neutrons from the overall mass number of 9.

There are 4 protons, so the atomic number is also 4. This atom is beryllium.

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