[csinha]

The question is: At 25 degrees celsius, the pH of an aqueous solution of benzoic acid, pKa = 4.202 is measured (at equilibrium) to be 3.61.

What is the equilibrium concentration of the conjugate base?

This is a multipart question but I listed the one I am having trouble with. Previous question asked to find concentration of H3O+; since pH is given it is just 10^-3.61 but would the concentration of the conjugate base not be equal to the concentration of H3O+?

[Borek]

would the concentration of the conjugate base not be equal to the concentration of H3O+?

It would in this case. Note that it doesn't have to be true for diluted solutions, when concentration of H⁺ from water autodissociation starts to play an important role.