Hello, I really need help on this. I don't understand it.

B is the answer to the question

The closer the atoms are to becoming ionic the more highly dense the negatively charged side gets.

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).