Energy difference between actual structure of compound and most stable resonating structure having least energy is called:

The correct option is Resonance energy.

Step-by-Step Explanation:

1. Understanding Resonance:
In chemistry, some molecules cannot be represented adequately by a single Lewis structure. Instead, we describe them using multiple contributing structures called resonating structures (or canonical forms).

2. Resonance Hybrid:
The actual structure of the molecule is a hybrid of all these resonating structures and is known as the resonance hybrid. The actual structure is always more stable and has lower energy than any of the individual resonating structures.

3. Defining Resonance Energy:
Among the various resonating structures, there is one that is the most stable (i.e., has the least energy). The difference in energy between the actual structure of the compound (the resonance hybrid) and this most stable resonating structure is defined as the Resonance Energy.
Mathematically, it can be represented as:
$\text{Resonance Energy}=\text{Energy of the most stable resonating structure}-\text{Energy of the actual structure}$
Because the actual structure is more stable, this difference represents the stability gained by the molecule due to resonance.