Heat up X or heat up x with potassium manganate?
Many (not all) redox reactions have high activation energy requirements. For instance, oxidation of alcohols to carboxylic acids require heat or reflux, for a visible (colour change of oxidizing agent) reaction to occur within a reasonable period of time.
>>> So is X a reducing agent or not a reducing agent? <<<
Note that, similarly with "acids" and "bases" (eg. water is simultaneously an acid and a base; conjugate acid is hydroxonium ion, conjugate base is hydroxide ion), there are many compounds that can be both reduced and oxidized (eg. H2O2, Fe2+, etc).
So X may be both a reducing agent and an oxidizing agent. You do not have sufficient data to ascertain this.
You can only deduce from the colour change that a chemical reaction has occurred between MnO4- and species X, which is in all likelihood a redox reaction (in which MnO4- has been reduced to Mn2+, MnO2, MnO4 2-, etc), resulting in a colour change.
Which brings me to another point. When you write "potassium manganate", there is ambiguity there. You may be penalized in the exams.
Latin Names versus Stock Names
| Permanganate | MnO4- | VII | violet |
| Manganate | MnO42- | VI | green |
| Hypomanganite | MnO43- | V | blue |
| Manganite | MnO44- | IV | brown |
The oxidizing reagent most commonly encountered at 'O' and 'A' levels, is potassium manganate(VII) (stock name) aka potassium permanganate (latin name).