50.0 grams of radium-233 has a half-life of 30.0 seconds. How many grams of radium-233 would remain after 3.00 minutes? (Answer with numbers only. 3 significant figures. No units.

The answer for #3 is c but i don't know why

If the particles in a sample of matter have an orderly arrangement and move only in place, the sample is a

Select all of the statements which are true. electrons are located in shells or orbits around the atom. electrons orbit slowly around the atom. electrons travel in one flat path around the nucleus of an atom. the valence of an atom is determined by the number of electrons in the atom's outermost shell.