All capacitors have value C. Below are the equivalent capacitances:

(a) Between points 1 and 2:

Equivalent capacitance = 15/11 · C. (Correct) — found by applying 1 V between 2 and 1 and calculating total charge.

(b) Between points 3 and 6:

Equivalent capacitance = 5/3 · C. (Correct) — put 1 V between 3 and 6 and evaluate charges on the network.

(c) Between points 1 and 3:

Equivalent capacitance = 15/14 · C. (Correct) — result from the same node-voltage method or careful reduction.

(d) Between points 3 and 5:

Option (d) claims 14/15 · C, which is incorrect. The actual value (by calculation) is 15/14 · C.

A reliable way is to apply 1 V across the chosen terminals, solve node-voltage relations to find charges on capacitors and sum the total charge Q. Then Ceq=Q (since V=1). This avoids mistakes in series/parallel reductions for symmetric networks.