Class JEE Mathematics Sets, Relations, and Functions Q #1012
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4 Marks 2025 JEE Main 2025 (Online) 23rd January Morning Shift MCQ SINGLE
Let $R = \{(1, 2), (2, 3), (3, 3)\}$ be a relation defined on the set $\{1, 2, 3, 4\}$. Then the minimum number of elements, needed to be added in $R$ so that $R$ becomes an equivalence relation, is:
(A) 9
(B) 8
(C) 7
(D) 10
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Correct Answer: C
Explanation
For $R$ to be an equivalence relation on $A = \{1, 2, 3, 4\}$, it must be reflexive, symmetric and transitive.

1. **Reflexive:** $R$ must contain $(1, 1), (2, 2), (3, 3), (4, 4)$. Since $(3,3)$ is already in $R$, we need to add $(1, 1), (2, 2), (4, 4)$.

2. **Symmetric:** $R$ must contain $(2, 1)$ and $(3, 2)$ because it contains $(1, 2)$ and $(2, 3)$.

3. **Transitive:** Since $(1, 2)$ and $(2, 3)$ are in $R$, $(1, 3)$ must also be in $R$. And since we added $(3,2)$ now we must add $(1,2)$. Which already exists.

So, the minimum elements to be added are:
$(1, 1), (2, 2), (4, 4), (2, 1), (3, 2), (1, 3)$.

Therefore, the minimum number of elements to be added is $7$.

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