Ahalf life of cobalt is 5.27years. approximately how much a 399 g sample will remain after 20 years?

Which element is least likely to undergo a chemical reaction

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

Jenny places a strip of ph paper into a solution. when she removes the ph paper, it has turned yellow-green. what should jenny do next to determine the ph of her solution? a. use a different testing method because the ph paper should not change colors b. place the ph paper into a machine that reads the ph of the solution c. compare the ph paper's color with the color of ph paper from another solution d. compare the ph paper's color with a chart of colors and ph ranges