The correct sentence is: Khalid is As tall as, if not taller than Naveed.
The phrase "as tall as, if not" is used to compare Khalid's height to Naveed's, suggesting that Khalid is at least as tall as Naveed, and possibly taller.
The term “healthier” is the comparative form of the term “healthy,” meaning we use it when we are making a comparison. Examples: Apples are healthier than cupcakes.