Explanation:

A binary tree is a tree data structure in which each node has at most two children, referred to as the left child and the right child. The number of nodes of degree 2 in a binary tree can be determined by counting the number of nodes with two children.

Let's analyze the given options:

a) log2n: This option suggests that the number of nodes of degree 2 is logarithmic with respect to the number of leaf nodes. However, this is not necessarily true. The number of nodes of degree 2 can vary depending on the structure of the tree, and it is not directly related to the number of leaf nodes.

b) n - 1: The number of nodes of degree 2 in a binary tree is always one less than the total number of nodes in the tree. This is because, in a binary tree, each node has at most two children. Therefore, if a binary tree has n nodes in total, the maximum number of nodes of degree 2 is n - 1.

c) n: This option suggests that the number of nodes of degree 2 is equal to the total number of nodes in the tree. This is incorrect because not all nodes in a binary tree have two children. Only some nodes, specifically the internal nodes, have two children.

d) 2n: This option suggests that the number of nodes of degree 2 is twice the total number of nodes in the tree. This is incorrect because each node in a binary tree can have at most two children. Therefore, it is not possible for the number of nodes of degree 2 to be greater than the total number of nodes.

Conclusion:

The correct answer is option b) n - 1. The number of nodes of degree 2 in a binary tree is always one less than the total number of nodes in the tree.