Correct answer: g/4
The breaking strength of the branch is 75% of the monkey's weight, i.e., 0.75mg. The net force acting on the monkey is the difference between its weight (mg) and the tension in the branch (T). For the branch to not break, T ≤ 0.75mg. Using Newton's second law, mg - T = ma. Substituting T = 0.75mg, we get mg - 0.75mg = ma, which simplifies to 0.25g = a. Thus, the minimum acceleration is g/4.