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NCERT Class XI Chemistry Structure of Atom Solutions

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Question : 22 of 67
Marks: +1, -0
Which of the following are isoelectronic species i.e., those having the same number of electrons?
Na+,K+,Mg2+,Ca2+,S2−,Ar\mathrm{Na}^{+}, \mathrm{K}^{+}, \mathrm{Mg}^{2+}, \mathrm{Ca}^{2+}, \mathrm{S}^{2-}, \mathrm{Ar}
Solution:  
Species Number of electrons
Na+\mathrm{Na}^{+} 11 - 1 = 10
K+\mathrm{K}^{+} 19 - 1 = 18
Mg2+\mathrm{Mg}^{2+} 12 – 2 = 10
Ca2+\mathrm{Ca}^{2+} 20 – 2 = 18
S2−\mathrm{S}^{2-} 16 + 2 = 18
Ar\mathrm{Ar} = 18
Thus Na+\mathrm{Na}^{+} and K+,Mg2+,Ca2+,S2−\mathrm{K}^{+}, \mathrm{Mg}^{2+}, \mathrm{Ca}^{2+}, \mathrm{S}^{2-} and Ar have the same number of electrons.
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