Does kryptonite kill superman instantly?

The only verified source supplied is a general overview of Superman’s creation and history. It mentions that Superman is a superhero with extraordinary powers but does not discuss any substances that might harm him. Kryptonite is a fictional element that has appeared in various Superman stories, yet the evidence here does not describe its properties or its impact on the character. Because the data set lacks any mention of kryptonite, we cannot assert whether contact with it results in instant death, gradual weakening, or any other consequence. Therefore, based solely on the available evidence, the answer must be that the question cannot be answered affirmatively or negatively.