If a particular reactant is involved in the slowest step of a multi-step reaction what will be the effect of?

Question

reaction what will be the effect of increasing its concentration?

the reaction rate will always decrease
the reaction rate will usually decrease
the reaction rate will always increase
the reaction rate will usually increase

Answer 1

The reaction rate will usually increase. We can't say "always" because the particular reactant may not be the limiting reagent in the slow step. In fact, I wouldn't even say "usually." I would just say "sometimes." Or I would say "The reaction rate will remain constant or increase." If the particular reactant was the limiting reagent, then the reaction rate will increase. If the particular reactant was not the limiting reagent, then the slow reaction step still cannot take place any faster; the limiting reagent must have an increased concentration in order for this to happen.

Answer 2

Reaction rate will usually increase.

Sometimes you can have saturation.