A 'limiting reactant' is the one, which decides the __________ in the chemical reacation.

ANS:B - conversion

A limiting reactant is the one that determines the maximum amount of product that can be formed in a chemical reaction. It is determined by stoichiometry, specifically by comparing the mole ratios of the reactants involved in the reaction. So, none of the options provided ("equilibrium constant," "conversion," or "rate constant") accurately describe what a limiting reactant determines in a chemical reaction. Instead, the correct answer is simply "none of these."