What are 3 characteristics of a mixture?

The substances in a mixture can be separated using physical methods such as filtration, freezing, and distillation.

There is little, see Enthalpy of mixing, or no energy change when a mixture forms.

Mixtures have variable compositions, while compounds have a fixed, definite formula.

Explanation:

< > according to newton's third law of motion, forces always act in equal but opposite pairs. another way of saying this is for every action, there is an equal but opposite reaction.< >

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.