Just Remember one important formula here,
X = L(N-1) +1
X -> No. of internal nodes
L -> No. of leaf nodes
N -> value of ‘N’ of any N-ary tree.
In the given question it is simply asking to find the Total number of internal nodes in the binary tree because if you delete any internal node of a binary tree then it will split the graph into 2 parts or disconnect the graph.
Binary tree is a 2-ary Tree.
Putting in equation,
X = L(2-1) + 1
X = L + 1 ------> eqn (i)
Now we can form another equation from the data given in the question,
It’s given that there are total ‘n’ nodes.
So, No. of internal nodes + No. of Leaf nodes = n
-> X + L = n ---------> eqn (ii)
Solving eqn (i) & (ii) for the value of ‘X’,
X = (n+1)/2
So option C is the correct answer.