Q131 / 200 · MHT CET - Medical 2026 (21 April Shift 2) · Chemistry
Which of the following ions has the highest ionic radii?
- Correct answerA$\text{Cr}^{3+}$
- B$\text{Mn}^{3+}$
- C$\text{Fe}^{3+}$
- D$\text{Co}^{3+}$
Solution
The given ions belong to the $3d$ transition series and possess a $+3$ charge.
As we move from left to right across a period, the atomic number increases, resulting in an increased nuclear charge. The additional electrons enter the inner $d$-orbital, which offers poor shielding.
This leads to an increase in the effective nuclear charge, which strongly attracts the valence shell electrons towards the nucleus and causes a gradual decrease in ionic radii.
The atomic numbers of the given elements are $Cr (24)$, $Mn (25)$, $Fe (26)$, and $Co (27)$.
Therefore, the order of ionic radii for the $+3$ ions is $Cr^{3+} > Mn^{3+} > Fe^{3+} > Co^{3+}$.
$Cr^{3+}$ has the highest ionic radius among the given options.
Answer: $\text{Cr}^{3+}$
As we move from left to right across a period, the atomic number increases, resulting in an increased nuclear charge. The additional electrons enter the inner $d$-orbital, which offers poor shielding.
This leads to an increase in the effective nuclear charge, which strongly attracts the valence shell electrons towards the nucleus and causes a gradual decrease in ionic radii.
The atomic numbers of the given elements are $Cr (24)$, $Mn (25)$, $Fe (26)$, and $Co (27)$.
Therefore, the order of ionic radii for the $+3$ ions is $Cr^{3+} > Mn^{3+} > Fe^{3+} > Co^{3+}$.
$Cr^{3+}$ has the highest ionic radius among the given options.
Answer: $\text{Cr}^{3+}$
Hence, the correct answer is option: 'A'.