What imaginary line marks the southern end of the tropical zone

The transfer of heat through the movement of a gas or liquid a. convection b. conduction c. radiation

When electrons are added to the outermost shell of a carbon atom, it forms--an anion that has a larger anion that has a smaller cation that has a larger cation that has a smaller radius.

If you put a helium-filled balloon in the refrigerator, what will happen?