Help me get this right

Which substances have the lowest melting points: ionic covalent, or metallic

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.

Convert the temperature of dry ice, –77 ∞c, into degrees fahrenheit and kelvin.