What is the significant figure of 5,000,000,000,000

Asample of radium-226 will decay 1/4 of its original amount after 3200years. what is the half-life of radium-226?

Word equation for k(s) +h2o(l) yield koh (aq) + h2

Water is initially present in a state where its molecules are far apart. during a change of state, its molecules slow down. which change of state has most likely taken place? from a gas to a liquid from a liquid to a gas from a solid to a liquid from a gas to a plasma