What is the difference Between Andaman and Nicobar Islands
The easiest way to put this up is that Nicobar island hosts Nicobarese tribe. These tribes have many things in common as that of mongoloids. Nicobar island faced a lot of devastation in 2004, Tsunami. Government later provided help to people who lost their loved ones in Tsunami. Considering the sanctity of the tribes, government of Andaman Islands does not allow tourist to visit this island. You can visit this destination only for work related things. Even locals in Port Blair, the capital of Andaman Islands are not allowed to visit this location just for any reasons.
Secondly, Nicobar Island hosts a naval base, which guards south east borders of India. Its not open for travelers as well.