A group of 2^n−1 routers are interconnected in a centralized binary tree with a router at each tree node . Router 1 communicates with Router j by sending a message to the root of the tree. The root then sends a message back down to j Derive an approximate expression for the minimum number of hops per message for large N , assuming that all the router pairs are equally likely

1). 2N−4

2). N−4/2

3). N−4/2

4). N−4