How many moles of H2SO4 are needed to make 285 mL of .750 M solution?

Which of these conditions most likely produces an unstable isotope?

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.

Which change to the system wood cause the freely-moving piston to lower?