To negate something is to:

To negate something means to deny or make it invalid; it involves asserting that the statement or proposition is false. This process of contradiction directly challenges the truth or existence of whatever is being negated. Therefore, saying that to negate is to contradict its validity accurately captures the essence of negation.

The other options describe approaches that do not align with the meaning of negation. Acknowledging the truth of something (the first option) indicates acceptance rather than denial, while reinforcing its importance (the third option) suggests support and affirmation instead of contradiction. Leaving something intact (the fourth option) implies no change or challenge at all, which is contrary to the concept of negation. Thus, the choice that best describes the act of negation is indeed the one that highlights contradiction.