Which of the following is the last required attribute of all photovoltaic cells to convert sunlight into energy?

Which of these conditions most likely produces an unstable isotope?

If a solution had a ph of 7 what is the solution

Which of the following is an example of physical change not a chemical change? a) a log gives off heat and light as it burns. b) a tree stores energy from the sun in its fruit. c) a penny lost in the grass slowly changes color. d) a water pipe freezes and cracks on a cold night.