Select the odd family relationship from the following alternatives based on blood relation versus relation by marriage.

Introduction / Context:
This aptitude question tests your understanding of basic family relationships and how they are classified into blood relations and relations created through marriage. Such questions are common in reasoning sections of competitive exams and help to check how clearly you understand family trees and generational links.

Given Data / Assumptions:

• Four relationship terms are given: Mother-in-law, Nephew, Grandson, Great grandfather.
• You are asked to select the relationship that is different from the other three.
• Assume standard definitions of family relations based on common usage in family trees.

Concept / Approach:
The key idea is to classify each option as either a blood relation or a relation by marriage. Blood relations are directly connected by birth, such as parent, child, or grandparent. A relation by marriage is created due to a spouse, such as mother-in-law, father-in-law, brother-in-law, and so on. Once we classify each option, we identify which one does not fit the majority pattern.

Step-by-Step Solution:
Step 1: Note that a nephew is the son of your brother or sister, so it is a blood relation. Step 2: A grandson is the son of your son or daughter, which is also a direct blood relation. Step 3: A great grandfather is the father of your grandfather or grandmother, which again is a direct blood relation that extends one more generation upward. Step 4: A mother-in-law, however, is the mother of your spouse, which is a relation created by marriage, not by direct blood. Step 5: Therefore, among the four, three are pure blood relations and one is a marriage-based relation.

Verification / Alternative check:
Another way to check is to imagine a family tree starting from yourself. Your nephew, grandson, and great grandfather can all be located by tracing up or down through parents and children only. Mother-in-law, on the other hand, appears only when you introduce a spouse into the family tree. This confirms that it is the only relation that is not purely blood based.

Why Other Options Are Wrong:

• Nephew: This is a blood relation through your siblings, so it matches the pattern of blood relatives.
• Grandson: This is a direct blood relation to a younger generation, so it is similar to other blood relations.
• Great grandfather: This is also a direct blood relation but in an older generation, so it still fits the blood relationship pattern.

Common Pitfalls:
Many learners focus only on the generational difference and may think that great grandfather is different because it is farther away in the family tree. However, the question is about odd one out, and the stronger and more logical classification is blood relation versus relation by marriage. Overlooking this difference can lead to the wrong choice.

Final Answer:
Mother-in-law