Hey Kunal! 

The cornea question was ambiguous for sure. As the history says in such cases they usually give bonus marks so this time also the chances are bright that they will give bonus marks. If  you dig upon this topic you will learn that it has two answers one is partially correct and the other one is absolutely correct. Let's see how

• Option 1 and option 4 can not be true
• Coming to option 3,the covering of the eye ball is not cornea; its mainly sclera. Cornea only covers one-third part. And the reason for it being partially correct is that it has collagen (which is a protein itself) and it does cover some part. {Partially correct}
• Coming to option 2, It has dense collagen. It is Avascular { oxygen dissolved in tears secreted from lacrimal gland(exocrine) provide nutrition to it}. And to seal the deal, it is the most sensitive portion of the eye.{correct in all way}

Thank you