Hookes law is a fundamental law of nature that describes the relationship between the deformation and the applied force of an elastic body. It states that, within the elastic limit, the deformation or strain of an elastic material is proportional to the applied force or stress. However, Hookes law does not hold good beyond a certain limit. The correct option for this limit is B, the limit of proportionality.

Explanation:

Limit of proportionality is defined as the maximum stress or force that can be applied to a material such that the stress-strain relationship remains linear. Beyond this limit, the stress-strain relationship becomes nonlinear, and the material begins to show plastic deformation. At this point, Hookes law no longer holds true.

To understand this concept better, let us consider the stress-strain curve of a typical metallic material. The curve can be divided into several regions based on the response of the material to applied stress.

1. Elastic Region: In this region, the material behaves elastically, and the deformation is proportional to the applied force. Hookes law holds good in this region.

2. Yield Point: Beyond the elastic region, the material enters the plastic region, and it begins to deform permanently. The yield point is defined as the point where the material begins to show plastic deformation. At this point, Hookes law no longer holds good.

3. Plastic Region: In this region, the material undergoes permanent deformation, and the stress-strain relationship is nonlinear.

4. Ultimate Tensile Strength: The maximum stress that a material can withstand before it breaks is called the ultimate tensile strength.

In conclusion, Hookes law holds good up to the limit of proportionality, which is the point beyond which the stress-strain relationship becomes nonlinear. Beyond this point, the material begins to undergo plastic deformation, and Hookes law is no longer valid.