In a family relation puzzle, it is given that (i) M is the brother of N, (ii) B is also a brother of N, and (iii) M is the brother of D. Based on these statements alone, which of the following relationships is definitely true?

Introduction / Context:
This verbal reasoning question is about blood relations, where you must decide which statement is definitely true from a set of given family relationships. Such questions are common in aptitude and competitive exams, and they test whether you can distinguish between what is possible and what is guaranteed by the information.

Given Data / Assumptions:

• M is the brother of N. This means M is male and M and N are siblings.
• B is the brother of N. This means B is male and B and N are siblings.
• M is the brother of D. This means M is male and M and D are siblings.
• Unless otherwise stated, reasoning questions normally assume that all siblings mentioned as brothers of the same person are part of the same nuclear family.

Concept / Approach:
The key idea is to understand what is certain and what is only possible. From the data, M and B are both described as brothers of N, so they are male children of N's parents. Under standard exam assumptions, this means M and B share the same parents and are therefore brothers of each other. The gender of N and D is not specified, so any option that tries to label them as brothers is not definitely true. We must pick the one relationship that follows inevitably from the shared parentage and given brother statements.

Step-by-Step Solution:
Step 1: From M is brother of N, conclude that M and N are siblings and that M is male.Step 2: From B is brother of N, conclude that B and N are siblings and that B is male.Step 3: In typical blood relation puzzles, when two people are brothers of the same person, they are treated as children of the same parents unless explicitly told otherwise.Step 4: Therefore, M and B are both sons of N's parents and hence are brothers of each other.Step 5: This makes the statement M is brother of B definitely true.

Verification / Alternative check:
Imagine a simple family: parents P1 and P2 have three children N, M and B. M is a brother of N, and B is also a brother of N. It is automatically true that M and B are brothers of each other. Now add D as another child of the same parents to satisfy M is brother of D. The relationship between N and D or the exact gender of N and D is not fixed by the statements, but the relationship between M and B as brothers remains guaranteed in every valid arrangement.

Why Other Options Are Wrong:
N is the brother of B is not definitely true because N's gender is never specified. N could be male or female.N is the brother of D is also uncertain: we do not know either N's gender or whether D and N are definitely siblings under stricter interpretations.D is the brother of M assumes that D is male, but the data only tell us that M is brother of D, not that D is a brother.B is the brother of D would be true only if we assume extra information about how D is connected to N and the parents. It is not explicitly guaranteed.

Common Pitfalls:
A frequent mistake is to assume that if B is brother of N, then N must also be brother of B. However, this reverses the gender information: the phrase brother of N describes B, not N. Another error is to over interpret M is brother of D and conclude that D must be male. In these questions, pay close attention to who is being described as brother or sister, and do not assign gender where it is not explicitly given. Focus on what is logically forced across all consistent family structures.

Final Answer:
The only relationship that is definitely true in all valid family structures is that M is the brother of B.