My kid has this habit of biting his nails. How can I correct this habit of his?

Yes, nagging or punishing about this could actually have the opposite result. However, my elder one suffered a major infection as a result of constant nail biting, to the point that we almost had to get her operated. For my younger one who was also picking up the habit, I did a quick visit to the doc where he pointed out that biting nails could mean cutting off the tips (I know it sounds cruel, but we had to avoid any infection). Each time my younger one tried doing it, I would remind about the doc and it stopped permanently :)