Isoelectronic species are elements or ions that have the same, or equal number of electrons. This module explores that although isoelectronic species have the same number of electrons, they are different in their physical and chemical properties. 

Ya Correct Option is A) 👇👇👇👇👇👇Isoelectronic species means those species which have same no. of total electrons. In Option A) K+ [ K = 19 ,,,- 1 for positive charge => 19+ (-1) = 19- 1 = 18 ] ,,,,,,Ca^ 2+ [ Ca = 20 ,,> 20 - 2= 18 ] Sc^ 3+ [ Sc = 21 ,,,,,=> 21 - 3 = 18 ]Cl ^ - [ Cl = 17 ,,,=> 17 + 1 = 18 .] All Species have same no. of e hence they are isoelectronic species.👍👍👍⭐⭐⭐💯💯💯💯

Explanation:

Definition of Isoelectronic Species:
Isoelectronic species are atoms, ions, or molecules that have the same number of electrons.

Analysis of Option A:
- K: The atomic number of potassium (K) is 19. It has 19 electrons.
- Ca2+: The calcium ion (Ca2+) has a +2 charge, which means it has lost 2 electrons compared to the neutral calcium atom. Therefore, it has 18 electrons.
- Sc3+: The scandium ion (Sc3+) has a +3 charge, which means it has lost 3 electrons compared to the neutral scandium atom. Therefore, it has 17 electrons.
- Cl-: The chloride ion (Cl-) has a -1 charge, which means it has gained 1 electron compared to the neutral chlorine atom. Therefore, it has 18 electrons.

Comparison of Electron Counts:
- K: 19 electrons
- Ca2+: 18 electrons
- Sc3+: 17 electrons
- Cl-: 18 electrons

Conclusion:
From the analysis, it can be seen that all four ions in option A have the same number of electrons, i.e., 18 electrons. Therefore, option A represents the collection of isoelectronic species.

Analysis of Other Options:
Option B:
- Na: The atomic number of sodium (Na) is 11. It has 11 electrons.
- Ca2+: Already analyzed in option A. It has 18 electrons.
- Sc3+: Already analyzed in option A. It has 17 electrons.
- F-: The fluoride ion (F-) has a -1 charge, which means it has gained 1 electron compared to the neutral fluorine atom. Therefore, it has 10 electrons.

The electron counts for these ions are not the same, so option B does not represent a collection of isoelectronic species.

Option C:
- K: Already analyzed in option A. It has 19 electrons.
- Cl-: Already analyzed in option A. It has 18 electrons.
- Mg2+: The magnesium ion (Mg2+) has a +2 charge, which means it has lost 2 electrons compared to the neutral magnesium atom. Therefore, it has 10 electrons.
- Sc3+: Already analyzed in option A. It has 17 electrons.

The electron counts for these ions are not the same, so option C does not represent a collection of isoelectronic species.

Option D:
- Na: Already analyzed in option B. It has 11 electrons.
- Mg2+: Already analyzed in option C. It has 10 electrons.
- Al3+: The aluminum ion (Al3+) has a +3 charge, which means it has lost 3 electrons compared to the neutral aluminum atom. Therefore, it has 10 electrons.
- Cl-: Already analyzed in option B. It has 18 electrons.

The electron counts for these ions are not the same, so option D does not represent a collection of isoelectronic species.

Conclusion:
Option A is the correct answer because it represents a collection of isoelectronic species, as all four ions have the same number of electrons (18 electrons).