Six friends are sitting in a circle and are facing the centre of the circle. Deena is between Nandhu and Unni. Aby is between Biya and Betty. Nandhu and Biya are opposite to each other. Who is sitting right to Nandhu ?

Let's arrange the 6 positions around a circle facing the center.
1. Nandhu and Biya are opposite to each other. Let's place Nandhu at the bottom and Biya at the top.
2. Deena is between Nandhu and Unni. This leaves two possibilities for Deena (either immediate left or immediate right of Nandhu). Let's arrange them counter-clockwise such that Deena is to the immediate right of Nandhu, and Unni is next to Deena.
3. Aby is between Biya and Betty. Placing Aby and Betty in the remaining positions completes the circle satisfying all conditions.
In this configuration, Deena sits to the immediate right of Nandhu.