If the half-life of a radioactive substance is 500 million years and you have 48 atoms of it, how many half-lives will have passed by the time that 6 atoms of the substance remain? O A. 3
O B. 2
O C. 4
O D. 5

Earth's axis of rotation is tilted at an angle of 23.5 degrees. what is one change you would see on earth if its axis was not tilted?

There are two steps in the usual industrial preparation of acrylic acid, the immediate precursor of several useful plastics. in the first step, calcium carbide and water react to form acetylene and calcium hydroxide: cac2 (s) + 2h2o (g) → c2h2 (g) + caoh2 (s) =δh−414.kj in the second step, acetylene, carbon dioxide and water react to form acrylic acid: 6c2h2 (g) + 3co2 (g) + 4h2o (g) → 5ch2chco2h (g) =δh132.kj calculate the net change in enthalpy for the formation of one mole of acrylic acid from calcium carbide, water and carbon dioxide from these reactions. round your answer to the nearest kj .

Amatch has about 21 milligrams of red phosphorus coating the tip. how many atoms of phosphorus is this?