Which situation is the best analogy for the doppler effect?

Tell me the iupac name of the following compounds:

Which statement about hf is true? it is zero for any compound in its standard state. it is positive when the bonds of the product store more energy than those of the reactants. it is negative when a compound forms from elements in their standard states. it is zero for any element that is in the liquid state.

The fact that the total amount of energy in a system remains constant is a(n)