13. earth's surface area is 5.1 x 10^8 km², its crust has an average thickness of 35 km and an average density of 2.8 g/cm'. the two rarest (non-radioactive) elements in the crust are ruthenium and rhodium, each with an abundance of 1.0 x 10g/metric ton crust. what is the total mass of these two elements in the earth's crust? (1g = 1 x 10 metric ton)

that's what i got you can count the number of atoms

a. energy is absorbed in the reaction.

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.

nuclear fission produces elements that are heavier than helium.

the elements that are used in nuclear fission and their products are much heavier than helium.