Correct Answer - C
(c ) The equivalent network is
Clearly, the network of resistance is a balanced Wheatstone bridge. So `R_(AB)` is given by ltbRgt `(1)/(R_(AB)) = (1)/(3R) + (1)/(6R) = (2 + 1)/(6 R) = (1)/(2 R) implies R_(AB) = 2R`
For maximum power transfer `2 R = 4 Omega implies (4)/(2) = 2 Omega`
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