For a complex reaction the reaction progress curve
a)has several hills and valleys
b)has only one peak
c)is a flat line
d)shows energy vs. pressure

a) has several hills and valleys

Explanation: Elementary reactions are reactions which takes place in one single step and thus contains only a single peak.

Complex reactions are reactions which cannot take place in one step but takes place in a sequence of number of steps.

In a complex chemical reaction, the reactant molecules pass through different transition states due to bond breaking and bond making. Here the species stays for a very short period, usually called transition period of activated complex.

Explanation:

Scientists most especially chemists use the mole concepts through balanced chemical equations and molar masses to represent chemical reactions and account for the amount of substances.

The mole concept entails finding molar relationships between reactants and products in a chemical reaction. Mole connects difference chemical parameters and it is used in quantitative analysis of chemical reaction.

First, we work from the known to the unknown. The known is the specie whose mass or number of moles is given.

  Number of moles  =

After obtaining the number of moles, then go ahead to compared using the balanced reaction with that of the unknown. Then from them find the mass of the unknown.