if there are 30 g of Np-240 present, how much will remain after 9 hrs. Np-240 has a half-life of 1.0 hr

Compounds a and b react to form compounds c and d according to the equation: aa + bb → cc + dd. under which conditions will the rate law be given by the equation: rate = k[a]a[b]b? a. the reaction takes place in one step. b. the reaction is endothermic. c. the reaction is exothermic. d. the reaction involves more than one step.