1(xi)
Given below are four ions:
Cl-, Li+, Al3+, K+
Identify the pair of ions which have the same electronic configuration.
[Atomic number: Cl = 17, Li = 3, Al = 13, K = 19]
- (a)Cl- & Li+
- (b)Al3+ & K+
- (c)Cl- & K+
- (d)Li+ & K+
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Cl- & K+
Reason
- Chlorine has atomic number 17. Its neutral atom contains 17 electrons with the configuration 2, 8, 7. When it gains one electron to form Cl⁻, it has 18 electrons, giving the configuration 2, 8, 8 (the same as argon).
- Potassium has atomic number 19. A neutral K atom has the configuration 2, 8, 8, 1. When it loses one electron to form K⁺, it is left with 18 electrons, also giving the configuration 2, 8, 8.
Because both Cl⁻ and K⁺ possess 18 electrons and share the electron configuration 2, 8, 8, they form the required pair with identical electronic configurations.