Question

Find the true statements regarding a Ne atom with a mass number of 20 and an $O^{2-}$ ion with a mass number of 16?
A) They contain the same number of protons

B) They contain the same number of neutrons

C) They contain the same number of protons plus neutrons
D) They are isoelectronic

E) They are isomers

Answer 1

Hint: In order to solve this question, we have to know about the number of protons and neutrons of Ne and $\mathrm{O}^{2-}$ ion. From the mass number, we can easily find that because mass number is the total number of protons and neutrons.

Complete step by step answer:
Discussing option (A), we have that the number of protons of a Ne atom is $10 .$ The number of protons in $\mathrm{O}^{2-}$ ion is 6 protons. Hence they do not contain the same number of protons.
Discussing option (B), we have that the number of neutrons of a Ne atom is (Mass number-Number of protons) $=10 .$ But that is not for the case of $\mathrm{O}^{2-}$ ion because this is not a neutral atom, it is an anion. Thus the number of neutrons is $8 .$ Hence they do not contain the same number of neutrons.

Discussing option $(\mathrm{C}),$ we have the total number of protons and neutrons of $\mathrm{Ne}$ atom is $20 .$ But for $\mathrm{O}^{2-}$ ion, the total number of protons and neutrons is $14 .$ Hence they do not have the same number of protons plus neutrons.

Discussing option(D), we have the total number of electrons for Ne atom is $10 .$ But for $\mathrm{O}^{2-}$ ion, we have 10 electrons because in the $\mathrm{O}$ atom, it has 8 electrons. Thus it accepts 2 more electrons to form $\mathrm{O}^{2-}$ ion. Isoelectronic means the set has the same number of electrons. Hence they are isoelectronic.

Discussing option(E),isomers are those which share the same chemical formula but difference in structure. Clearly, $\mathrm{O}^{2-}$ ion and $\mathrm{Ne}$ atoms do not possess the same chemical formula. Hence, they are not isomers.
So, the correct answer is “Option D”.

Note: Do not confuse isomer with isoelectronic. Isoelectronic means the set has the same number of electrons. Isomers are those which share the same chemical formula but difference in structure.