Which is the right answer and why did you pick that answer?

B. 77%

the students that studied in the 4-5 hour range scored in the 70s. the ones that studied in the 6 hour range scored in the 80s.

I'd put 5 1/2 hours at around 80%, but the closest answer is the 77%

answer:

the position of equilibrium will shift to the left.

step-by-step explanation:

the general equation for the dissociation of a weak base is

b + h₂o   ⇌   bh⁺ + oh⁻

according to le châtelier's principle, when a stress is applied to a system at equilibrium, the system will respond in a way that tends to relieve the stress.

if you apply a stress by adding more bh⁺ or oh⁻,   the system will respond by moving in a direction that gets rid of the added ions.

the position of equilibrium will shift to the left, forming more of the undissociated base.