Answer
No, this set of values is impossible.
Work Step by Step
1. Is the atomic number equal to the number of protons?
- Yes, they are equal. (18)
2. Is the sum of the number of protons and neutrons equal to the mass number?
Sum: $18 + 40 = 58$
Mass number: 40
- No, they aren't equal ($58 \ne 40$).
- Therefore, this set of values is impossible.
