In the video about half-life, Ra-223 decays to Rn-219 by alpha decay with a half-life of 11 days. Assuming you start with 80 grams of Ra-223, how much would be left after 33 days? 5 grams 10 grams 20 grams 40 grams

Electric charge is what ? a. kinetic energy b. radiation c. discovery d. electricity

What effect would average population growth have on land usage? a. urban use of land would rise to more than 30 percent of available land. b. industrial use of land would rise to more than 30 percent of available land. c. the percentage of available land used as cropland would stay the same. d. cropland would fall to about 10 percent of available land.

Reactions in cells take place at about a. 40°c b. 0° c. 100°c d. 60°c