What is the difference between traffic lights with red arrows and those with solid red lights?

Red Arrows are used when there is a turning lane. Means there is a signal for more than one direction. Example would be one for the left turn, one for the right turn.
Solid red light means that it's a straight ahead.

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).