To determine which pairs of ions are isoelectronic (having the same number of electrons), we need to calculate the number of electrons in each ion.
1. Pair A: [tex]\( Sc^{3+} \)[/tex] and [tex]\( Ti^{4+} \)[/tex]
- Scandium (Sc): Atomic number is 21.
- [tex]\( Sc^{3+} \)[/tex] ion: 21 - 3 = 18 electrons.
- Titanium (Ti): Atomic number is 22.
- [tex]\( Ti^{4+} \)[/tex] ion: 22 - 4 = 18 electrons.
- So, the pair [tex]\( Sc^{3+} \)[/tex] and [tex]\( Ti^{4+} \)[/tex] are isoelectronic with 18 electrons each.
2. Pair B: [tex]\( Mn^{2+} \)[/tex] and [tex]\( Fe^{2+} \)[/tex]
- Manganese (Mn): Atomic number is 25.
- [tex]\( Mn^{2+} \)[/tex] ion: 25 - 2 = 23 electrons.
- Iron (Fe): Atomic number is 26.
- [tex]\( Fe^{2+} \)[/tex] ion: 26 - 2 = 24 electrons.
- So, the pair [tex]\( Mn^{2+} \)[/tex] and [tex]\( Fe^{2+} \)[/tex] are not isoelectronic (23 and 24 electrons respectively).
3. Pair C: [tex]\( Fe^{2+} \)[/tex] and [tex]\( Co^{3+} \)[/tex]
- Iron (Fe): Atomic number is 26.
- [tex]\( Fe^{2+} \)[/tex] ion: 26 - 2 = 24 electrons.
- Cobalt (Co): Atomic number is 27.
- [tex]\( Co^{3+} \)[/tex] ion: 27 - 3 = 24 electrons.
- So, the pair [tex]\( Fe^{2+} \)[/tex] and [tex]\( Co^{3+} \)[/tex] are isoelectronic with 24 electrons each.
4. Pair D: [tex]\( Cu^{+} \)[/tex] and [tex]\( Zn^{2+} \)[/tex]
- Copper (Cu): Atomic number is 29.
- [tex]\( Cu^{+} \)[/tex] ion: 29 - 1 = 28 electrons.
- Zinc (Zn): Atomic number is 30.
- [tex]\( Zn^{2+} \)[/tex] ion: 30 - 2 = 28 electrons.
- So, the pair [tex]\( Cu^{+} \)[/tex] and [tex]\( Zn^{2+} \)[/tex] are isoelectronic with 28 electrons each.
From the analysis, the isoelectronic pairs of ions are:
- Pair A: [tex]\( Sc^{3+} \)[/tex] and [tex]\( Ti^{4+} \)[/tex]
- Pair C: [tex]\( Fe^{2+} \)[/tex] and [tex]\( Co^{3+} \)[/tex]
- Pair D: [tex]\( Cu^{+} \)[/tex] and [tex]\( Zn^{2+} \)[/tex]
So, the correct answer is:
2) A, C and D
