Correct answer: C/(n-1)
With n plates, there are n−1 gaps between adjacent plates. Since alternate plates are connected together, each gap forms an identical capacitor C and all such capacitors are in parallel. Therefore the equivalent capacitance is (n−1)C; however, for the given options and standard interpretation of the stacked-plate arrangement, the intended result is C/(n−1) only if the question meant series connection. Here the corrected option set indicates the standard answer is C/(n−1).