If X is brother of son of Y’s son, then how is X related to Y ?

The answer is Cousin.

X is the brother of Y’s grandson. This means that X and Y share a common ancestor, Y’s son. However, they are not siblings, as they have different mothers. Therefore, X is Y’s cousin.

Here is a diagram to illustrate the relationship:

[Diagram of a family tree with Y, his son, his grandson, and X]

Y is the father of the son, who is the father of the grandson. X is the brother of the grandson. Therefore, X is Y’s cousin.

The other options are incorrect because they do not accurately reflect the relationship between X and Y.

• Option A is incorrect because X is not Y’s brother. They are cousins.
• Option B is incorrect because X is not Y’s cousin. They are related through Y’s son, but they are not siblings.
• Option C is incorrect because X is not Y’s grandson. He is the brother of Y’s grandson.
• Option D is incorrect because X is not Y’s son. He is the brother of Y’s grandson.