A sample of a radioactive isotope is 80 mg. What is the amount of radioactivity left after 3 half-lives? *
(1 Point)

Which part of earth’s surface receives the most direct rays from the sun? a) equator b) ocean c) poles d) mountains

How does a catalyst increase the speed of a reaction? a. the catalyst eliminates the activated complex stage, allowing products to form immediately. b. the catalyst lowers the energy level of the reactants, making it easier for them to react. c. the catalyst makes it easier for the activated complex to form, lowering the activation energy. d. the catalyst raises the energy level of the products, making the reaction finish sooner. reset next

Which symbol can be used to indicate the pressure at which a chemical reaction is carried out? 25°c 2 atm pa