JAMB Chemistry 2024 Paper

Concept:In a neutral atom, the number of electrons equals the atomic number $Z$, which is also the number of protons.The mass number is $A = Z + N$, where $N$ is the number of neutrons.Explanation:The mass number given is $A = 31$.So, $Z + N = 31$.Check each option to see which pair satisfies this condition.Option B: $16 + 31 = 47$, so it is incorrect.Option C: $15 + 31 = 46$, so it is incorrect.Option A gives electrons $= 15$, so $Z = 15$.Then neutrons $N = 31 - 15 = 16$.This matches $\mathrm{^{31}_{15}P}$, phosphorus-31, which is a stable neutral atom.Option D gives $Z = 16$ and $N = 15$, but that is not a stable isotope.Therefore, the required numbers are 15 electrons and 16 neutrons.Answer:A. 15 and 16