Question

What is the relation between an $Ne$ atom (mass number of $20$) and an $O^{2-}$ ion (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

Answer: (D)

They are isoelectronic

A Ne atom (mass number of 20) and an O2− ion (mass number of 16) are isoelectronic. Both contain 10 electrons.
Ne (Z = 10) has 10 electrons. O (Z=8) has 8 electrons. It gains two electrons to form oxide ion with $8+2=10$ electrons.