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).