The correct answer is option 1 Condition: Every node should have an odd number of descendants Descendant = odd Required: How many nodes available in the tree that have exactly one child Child = 1 Explanation: Let's understand it through examples 1) if n=1 (number of nodes =1) This root considered own descendant Descendant = 1= odd (Acceptable tree) Child =0 So, no node is present in the tree that has exactly one child → Fails the requirement 2)if take n=2 (number of nodes =2) Root node A has 2 descendant in both the graph Descendant = 2 = Even (Not Acceptable tree) 3)if take n=3 (number of nodes =3)