HCOOH
NaHCO\(_3\)
FeCO\(_3\)
H\(_2\)C\(_2\)O\(_4\)
Correct answer is D
It should be noted that for X to liberate CO\(_2\), X must be a carbonate or an oxalate. Since X decolorizes KMnO\(_4\), X must be an oxalate.
Therefore, X is H\(_2\)C\(_2\)O\(_4\).