The correct functional group X and the reagent/reaction condition Y in the following scheme are

Reduction of the metal centre in aqueous permanganate ion involves

The total number of contributing structure showing hyper-conjugation (involving C-H bonds) for the following carbocation is _________.

Among the following, the number of compounds that can react with PCl₅ to given POCl₃ is _____________.

O₂, CO₂, SO₂, H₂O, H₂SO₄, P₄O₁₀