The equilibrium constant for a chemical reaction is defined in terms of molar concentrations of products and reactants at equilibrium. For a general reaction: The equilibrium constant is: where represents the molar concentration of species in .
To find the units of , we analyze the units of the concentrations: - Concentration . - For each term , the unit is .
The units of are: Simplify: where is the change in the number of moles of gas (for gas-phase reactions, but here we consider concentrations for ).
However, the question does not specify a particular reaction, suggesting a case where is dimensionless. This occurs when , i.e., the sum of the stoichiometric coefficients of products equals that of reactants ( ). For example, in the reaction: Here, is dimensionless ( ).
Among the options, “dimensionless” fits this case. Without a specific reaction, we assume the question refers to an equilibrium where has no units, which is common in standard problems when .