How many half-life cycles must pass for only 25% of the original sample of Uranium-235 atoms to remain?

1) in saturated limewater, [h+ ]=3.98x10-13 m. a) find [oh]-/ b) what is the ph? / c) is the solution acidic, basic, or neutral? / 2) in butter, [h+ ]=6.0x10-7 m. a) find [oh]-/ b) what is the ph? / c) is the solution acidic, basic, or neutral? / 3) in peaches, [oh]=3.16x10-11 m a) find [h+ ]/ b) what is the ph? / c) is the solution acidic, basic, or neutral? / 4) during the course of the day, human saliva varies between being acidic and basic. if [oh]=3.16x10-8 m, a) find [h+ ]/ b) what is the ph? / c) is the solution acidic, basic, or neutral? /

If an atom has 12 protons and 13 neutrons

110 g of water (specific heat = 4.184 j/g c) and 100 g of a metal sample (specific heat = 0.397 j/g c) are heated from 25 degrees c to 75 degrees c. which substance required more thermal energy?