Hydrocarbons: explain question

A student carries out two experiments on separate samples of an unknown alkene, X.

In experiment 1, a sample of X is warmed with cold dilute acidified aqueous $\ce{KMnO4}$. The purple solution decolourises and a single organic product, Y, is formed.

In experiment 2, a separate sample of X is heated under reflux with hot concentrated acidified aqueous $\ce{KMnO4}$. The products are propanoic acid, $\ce{CH3CH2COOH}$, and carbon dioxide, $\ce{CO2}$.

(a) Identify the structural features of X that are consistent with the results of both experiments.

(b) The student then reacts propene with steam in the presence of a $\ce{H3PO4}$ catalyst. State the name of the organic product and the type of reaction.

(c) Explain why the reaction in (b) is described as an electrophilic addition.