How many half-lives are required for the concentration of reactant to decrease to 12.5% of its original value?

Which of the following observations indicates that there is a small, dense, positively charged part in the center of an atom? some uncharged particles are scattered by a gold foil. all uncharged particles are attracted towards a gold foil. all positively charged particles pass straight through a gold foil. some positively charged particles bounce back from a gold foil.

At 300 mm hg, a gas has a volume of 380 l, what is the volume at standard pressure

Once similarity and one difference between a mixture of elements and a mixture of compounds