How is a pure substance different than a mixture

The enthalpy of formation of water is -285.8 kj/mol. what can be inferred from this statement?

There are main groups in the modern periodic table of elements

Which of the following two events occur to create a sea breeze? select all that apply. warm air rises on the ocean and moves toward the land to cool warm air rises on land and moves toward the ocean to cool cool air moves from the ocean to be warmed by the land cool air moves from the land to be warmed by the ocean