Which one of the following sets of ions represents the collection of isoelectronic species? (Atomic nos. : F = 9, Cl = 17, Na = 11, Mg = 12, Al = 13, K = 19, Ca = 20, Sc = 21)

Structure of Atom PYQ — JEE Main 2004 · Shift 0 · Q58 with Solution

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Correct answer: C

Isoelectronic species are atoms/ions having the same number of electrons.
Let us calculate the number of electrons in each ion using: $\text{Number of electrons} = Z - \text{positive charge}$ for cations, and $\text{Number of electrons} = Z + \text{negative charge}$ for anions.

Check each option:

Option A: $K^+$ , $Cl^-$ , $Mg^{2+}$ , $Sc^{3+}$

$K^+$ : $19 - 1 = 18$
$Cl^-$ : $17 + 1 = 18$
$Mg^{2+}$ : $12 - 2 = 10$
$Sc^{3+}$ : $21 - 3 = 18$

Not all have the same number of electrons. So, A is incorrect.

Option B: $Na^+$ , $Ca^{2+}$ , $Sc^{3+}$ , $F^-$

$Na^+$ : $11 - 1 = 10$
$Ca^{2+}$ : $20 - 2 = 18$
$Sc^{3+}$ : $21 - 3 = 18$
$F^-$ : $9 + 1 = 10$

Two ions have 10 electrons and two have 18 electrons. So, B is incorrect.

Option C: $K^+$ , $Ca^{2+}$ , $Sc^{3+}$ , $Cl^-$

$K^+$ : $19 - 1 = 18$
$Ca^{2+}$ : $20 - 2 = 18$
$Sc^{3+}$ : $21 - 3 = 18$
$Cl^-$ : $17 + 1 = 18$

All have 18 electrons. So, C is correct.

Option D: $Na^+$ , $Mg^{2+}$ , $Al^{3+}$ , $Cl^-$

$Na^+$ : $11 - 1 = 10$
$Mg^{2+}$ : $12 - 2 = 10$
$Al^{3+}$ : $13 - 3 = 10$
$Cl^-$ : $17 + 1 = 18$

Three ions have 10 electrons, but $Cl^-$ has 18 electrons. So, D is incorrect.

Therefore, the collection of isoelectronic species is: $\boxed{K^+,\ Ca^{2+},\ Sc^{3+},\ Cl^-}$

So, the correct option is: $\boxed{\text{C}}$

Comparison with stored correct answer: Stored correct answer = C

My derived answer = C

Hence, they agree.

Structure of Atom question

Structure of Atom question

Option A: $K^+$ , $Cl^-$ , $Mg^{2+}$ , $Sc^{3+}$

Option B: $Na^+$ , $Ca^{2+}$ , $Sc^{3+}$ , $F^-$

Option C: $K^+$ , $Ca^{2+}$ , $Sc^{3+}$ , $Cl^-$

Option D: $Na^+$ , $Mg^{2+}$ , $Al^{3+}$ , $Cl^-$

More from Structure of Atom

Structure of Atom question

Structure of Atom question

Option A: $K^+$ , $Cl^-$ , $Mg^{2+}$ , $Sc^{3+}$

Option B: $Na^+$ , $Ca^{2+}$ , $Sc^{3+}$ , $F^-$

Option C: $K^+$ , $Ca^{2+}$ , $Sc^{3+}$ , $Cl^-$

Option D: $Na^+$ , $Mg^{2+}$ , $Al^{3+}$ , $Cl^-$

More from Structure of Atom

Option A: K+K^+K+, Cl−Cl^-Cl−, Mg2+Mg^{2+}Mg2+, Sc3+Sc^{3+}Sc3+

Option B: Na+Na^+Na+, Ca2+Ca^{2+}Ca2+, Sc3+Sc^{3+}Sc3+, F−F^-F−

Option C: K+K^+K+, Ca2+Ca^{2+}Ca2+, Sc3+Sc^{3+}Sc3+, Cl−Cl^-Cl−

Option D: Na+Na^+Na+, Mg2+Mg^{2+}Mg2+, Al3+Al^{3+}Al3+, Cl−Cl^-Cl−

More from Structure of Atom

Option A: K+K^+K+, Cl−Cl^-Cl−, Mg2+Mg^{2+}Mg2+, Sc3+Sc^{3+}Sc3+

Option B: Na+Na^+Na+, Ca2+Ca^{2+}Ca2+, Sc3+Sc^{3+}Sc3+, F−F^-F−

Option C: K+K^+K+, Ca2+Ca^{2+}Ca2+, Sc3+Sc^{3+}Sc3+, Cl−Cl^-Cl−

Option D: Na+Na^+Na+, Mg2+Mg^{2+}Mg2+, Al3+Al^{3+}Al3+, Cl−Cl^-Cl−

More from Structure of Atom

Option A: $K^+$ , $Cl^-$ , $Mg^{2+}$ , $Sc^{3+}$

Option B: $Na^+$ , $Ca^{2+}$ , $Sc^{3+}$ , $F^-$

Option C: $K^+$ , $Ca^{2+}$ , $Sc^{3+}$ , $Cl^-$

Option D: $Na^+$ , $Mg^{2+}$ , $Al^{3+}$ , $Cl^-$

Option A: $K^+$ , $Cl^-$ , $Mg^{2+}$ , $Sc^{3+}$

Option B: $Na^+$ , $Ca^{2+}$ , $Sc^{3+}$ , $F^-$

Option C: $K^+$ , $Ca^{2+}$ , $Sc^{3+}$ , $Cl^-$

Option D: $Na^+$ , $Mg^{2+}$ , $Al^{3+}$ , $Cl^-$