Which of the following are the characteristic properties of the manganate ion (MnO42−)?
(A) Tetrahedral geometry
(B) Purple color
(C) Diamagnetic
(D) Presence of two Mn = O bond
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A) and (D) only
Potassium manganate, \( \ce{K2MnO4} \), is made by fusing \( \ce{MnO2} \) with KOH in the presence of an oxidising agent. In the manganate ion, \( \ce{MnO4^{2-}} \), manganese is in the +6 oxidation state (x + 4(−2) = −2, so x = +6). Mn (Z = 25) is [Ar]3d54s2; removing six electrons (the two 4s and four of the 3d) leaves 3d1. The ion is tetrahedral and green, and it is stable only in alkaline solution. In neutral or acidic solution it disproportionates to permanganate:
\( \displaystyle \ce{3MnO4^2- + 4H^+ -> 2MnO4^- + MnO2 + 2H2O} \)
(A) Tetrahedral geometry — Correct. Mn is surrounded by four oxygen atoms arranged tetrahedrally.
(B) Purple color — Incorrect. The manganate ion is green. The purple colour belongs to the permanganate ion, \( \ce{MnO4^{-}} \).
(C) Diamagnetic — Incorrect. Mn(+6) has one unpaired 3d electron, so manganate is paramagnetic.
(D) Presence of two Mn = O bond — Correct. In the structure of \( \ce{MnO4^{2-}} \), two oxygen atoms are joined to Mn by double bonds and the other two carry the negative charges on single bonds.
NCERT (2026-27 edition):
Oxides and Oxoanions of Metals – …
