In which one of the following sets all species show disproportionation reaction?

Check each set for all species being capable of disproportionation:

Set (1): $\mathrm{ClO_4^-}$, $\mathrm{MnO_4^-}$, $\mathrm{ClO_2^-}$, $\mathrm{F_2}$

• $\mathrm{ClO_4^-}$: Cl = $+7$ (max) → cannot disproportionate ✗
• $\mathrm{MnO_4^-}$: Mn = $+7$ (max) → cannot disproportionate ✗
• $\mathrm{F_2}$: no positive OS → cannot disproportionate ✗

Set (2): $\mathrm{MnO_4^{2-}}$, $\mathrm{ClO_2^-}$, $\mathrm{Cl_2}$, $\mathrm{Mn^{3+}}$

• $\mathrm{MnO_4^{2-}}$: Mn = $+6$ → disproportionates to $\mathrm{MnO_4^-}$ (+7) and $\mathrm{MnO_2}$ (+4) ✓
• $\mathrm{ClO_2^-}$: Cl = $+3$ → disproportionates to $\mathrm{Cl^-}$ and $\mathrm{ClO_3^-}$ ✓
• $\mathrm{Cl_2}$: Cl = $0$ → disproportionates in alkaline medium ✓
• $\mathrm{Mn^{3+}}$: Mn = $+3$ → disproportionates to $\mathrm{Mn^{2+}}$ and $\mathrm{MnO_2}$ ✓ All four can disproportionate ✓

Set (3) and (4): Contain $\mathrm{MnO_4^-}$ (Mn = $+7$, max) or $\mathrm{Cr_2O_7^{2-}}$ (Cr = $+6$, max for Cr) or $\mathrm{F_2}$ → at least one cannot disproportionate ✗

Answer: Option (2)