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JEE Advanced levelSingle correct optionDifficulty 3 of 3qa127

A borax bead dipped in a manganese(II) salt becomes violet on cooling after heating in the oxidising flame; the colour is due to manganese(III) metaborate. Taking the borate environment as weak field (high-spin), the oxidation state of Mn in the violet bead and its spin-only magnetic moment (BM) are:

  1. A;
  2. B;
  3. C;
  4. D;

Answer: C

The violet bead contains , so Mn is +3, configuration . High spin means 4 unpaired electrons, so . The value belongs to Mn(II), to low-spin , and to Mn(IV).
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