Question

which of the following pairs of atoms/ions is isoelectronic?
o-2, s-2
cu, zn
na, na+1
br-1, kr

Explanation:

Step1: Recall the concept of isoelectronic species

Isoelectronic species have the same number of electrons.

Step2: Calculate the number of electrons for each option

• For \(O^{2 -}\): Oxygen has atomic number \(Z = 8\). For \(O^{2-}\), the number of electrons \(n_e=8 + 2=10\). For \(S^{2-}\): Sulfur has atomic number \(Z = 16\). For \(S^{2-}\), the number of electrons \(n_e=16+ 2 = 18\).
• For \(Cu\): Copper has atomic number \(Z = 29\), so the number of electrons \(n_e = 29\). For \(Zn\): Zinc has atomic number \(Z=30\), so the number of electrons \(n_e = 30\).
• For \(Na\): Sodium has atomic number \(Z = 11\), so the number of electrons \(n_e=11\). For \(Na^{+}\): The number of electrons \(n_e=11 - 1=10\).
• For \(Br^{-}\): Bromine has atomic number \(Z = 35\). For \(Br^{-}\), the number of electrons \(n_e=35 + 1=36\). For \(Kr\): Krypton has atomic number \(Z = 36\), so the number of electrons \(n_e = 36\).

Answer:

Br−1, Kr