Why is cracking a necessary part of the refinement of crude oil? A. It is not needed only recommended

B. because the demand for lead found in gasoline

C. because the demand for the mid-range hydrocarbons (C7-C12) found in gasoline exceeds the amount produced by the distillation
of crude oil

Iknow the answer is a but i don't know why

Reaction rate depends on how many molecules are coming into contact with each other with enough energy to react. increasing the temperature of the reactants will increase -

For a research project, a student decided to test the effect of the lead(ii) ion (pb2+) on the ability of salmon eggs to hatch. this ion was obtainable from the water‐soluble salt, lead(ii) nitrate, which the student decided to make by the following reaction. pbo(s) + 2 hno3(aq) → pb(no3)2(aq) + h2o losses of product for various reasons were expected, and a yield of 86.0% was expected. in order to have 5.00 g of product at this yield, how many grams of pbo should be reacted? (assume that sufficient nitric acid, hno3, would be used.)