PLEASE HELP ASAP Observations can sometimes indicate whether a change is chemical or physical. Which of the following is most likely evidence of a chemical change?

A substance no longer occupies the same volume.
A substance gives off heat and light.
An object changes state.
An object gets smaller.

Hydroelectricity provides about 7 percent of the electricity generated in the united states. (a) explain how a hydroelectric power plant converts energy stored in water into electricity. (b) identify two factors that determine the amount of electricity that can be generated by an individual hydroelectricity power plant. (c) describe the two main types of land-based hydroelectric power plants. (d) describe two economic advantages and two environmental disadvantages of hydroelectricity.