Which of the following denotes the number of nodes in a complete binary tree of level 5 ?

The correct answer is (d) 63.

A complete binary tree is a binary tree in which every level, except possibly the last, is completely filled, and all nodes in the last level are as far left as possible.

The number of nodes in a complete binary tree of level $n$ is given by the formula $2^n-1$.

For a complete binary tree of level 5, the number of nodes is $2^5-1=32-1=63$.

Option (a), 15, is the number of nodes in a complete binary tree of level 3.

Option (b), 25, is the number of nodes in a complete binary tree of level 4.

Option (c), 75, is the number of nodes in a complete binary tree of level 6.