Question

which of the following is a cation that is isoelectronic with f^- and o^{2-}?
a. ne
b. na^+
c. mg^{2+}
d. k^+
e. both b. and c.

Explanation:

Step1: Calculate the number of electrons in \(F^-\) and \(O^{2 -}\)

• For \(F^-\): Fluorine (\(F\)) has atomic number \(9\). \(F^-\) has \(9 + 1=10\) electrons.
• For \(O^{2 -}\): Oxygen (\(O\)) has atomic number \(8\). \(O^{2 -}\) has \(8+ 2 = 10\) electrons.

Step2: Calculate the number of electrons for each option

• For \(Ne\): Neon (\(Ne\)) has atomic number \(10\). But \(Ne\) is a neutral atom, not a cation.
• For \(Na^+\): Sodium (\(Na\)) has atomic number \(11\). \(Na^+\) has \(11-1 = 10\) electrons.
• For \(Mg^{2+}\): Magnesium (\(Mg\)) has atomic number \(12\). \(Mg^{2+}\) has \(12 - 2=10\) electrons.
• For \(K^+\): Potassium (\(K\)) has atomic number \(19\). \(K^+\) has \(19-1 = 18\) electrons.

Answer:

E. Both B. and C.