What is a first order effect?

Hint: We know that the first order effect is also known as the first order reaction of chemical kinetics. The order of a chemical reaction can be defined as the sum of power of concentration of reactants in the rate law expression is called the order of that chemical reaction. Reactions can be first order reaction, second order reaction, pseudo first order reaction etc.

Complete answer:
Order of reaction is determined by experiment. Although if we know rate law expression determined experimentally then we can determine order of reaction using rate law. Order of reaction can be an integer or fractional value. Kinetics in the first order arises where a constant proportion of the substance per unit time is removed. The removal rate is proportional to the quantity of medicine in the body. The larger the dosage, the higher the volume of substance extracted per unit of time.
The first order reaction will never be finished or completed at an infinite time and thus the x axis will never meet the decay graph line. We derived the first order rate law, and it is possible to extract the first order rate constant from this rate expression. In these reactions the rate of reaction depends on the concentration in these reactions the rate of reaction depends on the concentration of one reactant only. There can be many reactants in the reaction but concentration of only one reactant will affect the rate of reaction. Concentration of other reactants will have no effect on order of reaction.

Note:
Remember that those reactions which are not of first order but approximated or appear to be of first order due to higher concentration of the reactant/s than other reactants are known as pseudo first order reactions.