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Choose the correct option among the following in which the two species are both isoelectronic and isotopic? (Atomic numbers : Ca = 20, Ar = 18, Mg = 12, K = 19, Fe = 26)

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$^{40} {Ca}^{2+} {and}^{40} Ar$

$^{24} {Mg}^{2+} {and}^{25} Mg$

$^{39} K^{+} {and}^{40} K^{+}$

$^{56} {Fe}^{3+} {and}^{57} {Fe}^{2+}$

answer is C.

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Detailed Solution

Among the given species $39_{k^{+}} {and 40}_{k}$ have same number of electrons, thus are isoelectronic. Also, they have different number of neutrons, means they differ in their atomic masses hence option (c) is the correct answer.

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