Of the isomeric c5h11+ carbocations which one is the most stable?

Methyl groups are electron-donating, so the more CH3 groups attached to the +ve carbon, the more stable the carbocation becomes.

Polygon is ur

It is a mixture. simply put, a compound must be pure, that is, of only one chemical structure and composition. a mixture is made of different chemical substances (i.e. elements, molecules, compounds) that are not chemically bonded to each other, but instead physically grouped together, as in the case of gasoline (a homogeneous solution).