What does it mean for an element to have a -1 charge?

It's either 3 or that ,,but if not than choose 4

Organisms are more likely to be more preserved in mud than sand because mud is moist and wet, while sand is very dry.

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).