Q: 36 (NDA-I/2014)
question_subject:
Science
question_exam:
NDA-I
stats:
0,2,18,7,3,8,2
keywords:
{'isoelectronic ions': [0, 0, 0, 1], 'ca2': [0, 0, 0, 1]}
The correct answer is option 4, Ca2+ and S2-. Isoelectronic ions are ions that have the same number of electrons. In this case, Ca2+ and S2- both have 18 electrons.
Option 1 is incorrect because Na+ and K+ have different numbers of electrons. Na+ has lost one electron and K+ has lost two electrons.
Option 2 is incorrect because K and Mg2+ have different numbers of electrons. K has 19 electrons while Mg2+ has 10 electrons.
Option 3 is incorrect because Mg2+ and Ca2+ have different numbers of electrons. Mg2+ has 10 electrons while Ca2+ has 18 electrons.
Therefore, the only correct pair of isoelectronic ions is Ca2+ and S2- because they both have the same number of electrons, which is 18.