How many atoms are in a sample of uranium with a mass of 789 g.

Asample of radium-226 will decay 1/4 of its original amount after 3200years. what is the half-life of radium-226?

If anyone would be able to me out with these three questions it would be these are from the chem 2202 course.

What happens when an atom of sulfur combines with two atoms of chlorine to produce sci2? a. each chlorine atom shares a pair of electrons with the sulfur atom. b. an electron is transferred from each chlorine atom to the sulfur atom. c. an electron is transferred from the sulfur atom to each chlorine atom. d. each chlorine atom shares all its valence electrons with the sulfur atom.