CBSE Class 12 Mathematics Relations and Functions Q #2132
COMPETENCY BASED
APPLY
3 Marks Generic-Curriculum SA
Let $R$ be a relation defined over $N$, where $N$ is set of natural numbers, defined as "$m R n$ if and only if $m$ is a multiple of $n$, where $m, n \in N$." Find whether $R$ is reflexive, symmetric and transitive or not. [Delhi 2025]

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Detailed Solution

Step 1: Check for Reflexivity

A relation $R$ is reflexive if $a R a$ for all $a \in N$. Here, $m R n$ means $m$ is a multiple of $n$. Since every natural number $m$ is a multiple of itself (as $m = 1 \times m$), $m R m$ holds true for all $m \in N$. Thus, R is reflexive.

Step 2: Check for Symmetry

A relation $R$ is symmetric if $m R n \implies n R m$. Let $m=4$ and $n=2$. Here, $4 R 2$ is true because 4 is a multiple of 2. However, $2 R 4$ is false because 2 is not a multiple of 4. Since $m R n$ does not imply $n R m$, R is not symmetric.

Step 3: Check for Transitivity

A relation $R$ is transitive if $m R n$ and $n R p \implies m R p$. If $m$ is a multiple of $n$, then $m = kn$ for some $k \in N$. If $n$ is a multiple of $p$, then $n = jp$ for some $j \in N$. Substituting $n$, we get $m = k(jp) = (kj)p$. Since $kj \in N$, $m$ is a multiple of $p$. Thus, R is transitive.

Final Answer: The relation R is reflexive and transitive, but not symmetric.

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Pedagogical Audit
Bloom's Analysis: This is an APPLY question because the student must apply the formal definitions of equivalence relations to a specific set-theoretic relation.
Knowledge Dimension: CONCEPTUAL
Justification: The student must understand the underlying concepts of divisibility and the logical structure of relations rather than just memorizing facts.
Syllabus Audit: In the context of CBSE Class 12, this is classified as COMPETENCY. It tests the student's ability to verify properties of relations, which is a core competency in the Relations and Functions unit.