The original amount of radioactive substance is 10 grams. after several years, 2.5 gtams of the substance is remaining. how many half-lives havr passed since the mass of the subtance was 10 grams?

Why does the sun appear to be the brightest star in the sky? a- its apparent brightness is much greater than other stars. b- it burns more gas, making it brighter than any other star. c- it is the largest star in the galaxy, so it is the brightest star. d- its relative distance to earth is closer than the other stars.

According to each substances heat of fusion, which of the items below requires more heat to be added per gram of substance to go from solid to liquid? silver sulfur water lead

The volume of helium in a blimp is 6.28 x 10^9 millimeters. the density of helium in the blimp is .1786 kilogram/meter^3. find the mass of the helium in the blimp.