In HTTP request methods, which of the following methods is not idempotent ? 

In HTTP, an idempotent operation is one that can be applied multiple times without changing the result after the initial application. For instance, if you perform a GET or PUT request multiple times with the same parameters, the result will not change beyond the initial request. However, POST is not idempotent because it is used to submit data to be processed by the server, and each POST request can result in a different outcome. For example, submitting a POST request to create a new resource will create a new instance every time, even if the same request is sent multiple times. GET requests retrieve data and have no side effects, so they are considered idempotent. PUT requests are idempotent because they replace the resource at a specific URL with the same data every time, ensuring the same result on repeated requests. DELETE requests are idempotent because, after deleting a resource, subsequent DELETE requests for the same resource do not change the state (the resource is already deleted). PATCH requests are considered idempotent when they update a resource in a way that does not alter the resource's state with repeated requests, but the primary difference with POST is that PATCH typically modifies parts of a resource, while POST often creates new resources.