Which force keeps the planets in orbit?

1. gravity
2.kinetics
3.mass
4.friction

Which of these conditions most likely produces an unstable isotope?

A50.0g sample of liquid water at 0.0 c ends up as ice at -20.0 c. how much energy is involved in this change?

If a molecule with a molecular formula of c13h18 is treated with an excess of h2 in the presence of finally divided pt metal under conditions required for maximum hydrogenation of the molecule to give a molecule with a formula c13h24, how many rings are in the molecule?