To understand why the correct answer is option 'C', let's break down the problem and analyze it step-by-step.

1. Understanding the Electrical Network:
An electrical network consists of nodes (also called vertices) and branches (also called edges). Nodes represent points where the branches intersect, and branches represent the connections between the nodes. In this problem, we are given that the network has 4 nodes and 7 branches.

2. Tree in an Electrical Network:
In graph theory, a tree is a connected graph without any cycles. In an electrical network, a tree represents a set of branches that form a closed loop, where every node is connected to every other node in the network.

3. Choosing a Tree:
To determine the number of links (l) with respect to the chosen tree, we need to consider the concept of links. In an electrical network, a link is a branch that is not present in the chosen tree. In other words, it is a branch that can be removed without disconnecting any nodes.

4. Number of Links:
To find the number of links, we need to determine the minimum number of branches required to form a tree in the given electrical network.

According to the formula for trees in a graph, the minimum number of branches required to form a tree in a network with n nodes is n-1. In this case, we have 4 nodes, so the minimum number of branches required for a tree is 4-1 = 3.

Therefore, the number of links (l) with respect to the chosen tree is the total number of branches (7) minus the minimum number of branches required for a tree (3), which gives us l = 7 - 3 = 4.

Hence, the correct answer is option 'C', which states that the number of links, with respect to the chosen tree, is 4.