Often, if an investigator needs to add a very small amount of a reagent to a chemical reaction, they will first do a serial dilution as opposed to measuring the chemical directly. Why

The chemical reagents may be defined as the substance necessary to carry out the chemical reactions. The reagents can be consumed fully or partially during the chemical reaction.

The chemical reagents are needed to be diluted serially if they are measured directly without any dilution because this might produce  the faulty colors  an can give incorrect result during the  spectrophotometer. The serial dilution is important to get the correct optical density.

the correct answer is b

it provides an alternative energy pathway for the reaction to proceed.

a catalyst is a substance that speeds up the rate of a chemical reaction but is not consumed during the course of the reaction.

catalysts increase the rate of reaction without being used up. they do this by lowering the activation energy needed. with a catalyst, more collisions result in a reaction, so the rate of reaction increases. different reactions need different catalysts.

a catalyst works by providing an alternative reaction pathway to the reaction product. the rate of the reaction is increased as this alternative route has a lower activation energy than the reaction route not mediated by the catalyst.