<p>To an acidic solution of an anion, a few drops of&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>K</mi><mi>M</mi><mi>n</mi><msub><mi>O</mi><mn>4</mn></msub></math>&nbsp;solution are added. Which of the following, if present, will not decolourise the&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>K</mi><mi>M</mi><mi>n</mi><msub><mi>O</mi><mn>4</mn></msub></math>&nbsp;solution?</p>