$\left[\mathrm{MnO}_{4}\right]^{-}$is deep purple in colour whereas $\left[\mathrm{ReO}_{4}\right]^{-}$is colourless. This is due to greater energy required for
(a)d-d transitions in the Re compound compared to the Mn compound
(b)d-d transitions in the Mn compound compared to the Re compound
(c)charge transfer from O to Re compared to O to Mn
(d)charge transfer from O to Mn compared to O to Re
Answer
Answer: C ✓ checked by 4AB · confidence high
Explanation
Both are d⁰; colour comes from O→M LMCT. The 5d orbitals of Re(VII) lie higher than the 3d of Mn(VII), so the O→Re charge transfer needs more energy and falls in the UV, leaving ReO₄⁻ colourless.