(a) A pair of isotopes of chlorine is ³⁵₁₇Cl and ³⁷₁₇Cl. The atomic number of both the isotopes is the same 17. So, the electronic configuration of both these isotopes will be 2, 8, 7.

(b) A pair of isobars is ⁴⁰₁₈Ar and ⁴⁰₂₀Ca. The atomic number of orgon (Ar) is 18, so its electronic configuration will be 2, 8, 8. The atomic of calcius (Ca) is 20, so its electronic configuration will be 2, 8, 8, 2.