Q.If R is the relation "less than" from A={1,2,3,4,5} to B={1,4,5}, find the set of ordered pairs corresponding to R. Also define this relation from B to A.
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🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — Relation Properties
Properties of a Relation
A relation R on a set A pairs elements of A with one another. Some relations behave in regular, predictable ways, and we name these behaviours properties. Three matter most for CBSE Class 12 — reflexive, symmetric, transitive (together they build an equivalence relation); a fourth, antisymmetric, is worth knowing for order relations.
Reflexive — everything relates to itself
R is reflexive if aRa for every a∈A. "Has the same age as" is reflexive; "is taller than" is not. If even one element misses its self-pair, reflexivity fails: on {1,2,3}, {(1,1),(2,2)} is not reflexive because (3,3) is absent.
Symmetric — the relation runs both ways
R is symmetric if aRb⟹bRa. "Is married to" is symmetric; "is taller than" is not. Symmetry does not demand that every pair be related — only that any pair which appears also appears reversed. So {(1,2),(2,1),(3,3)} is symmetric, but {(1,2),(2,1),(1,3)} is not, since (3,1) is missing.
Transitive — relations chain
R is transitive if aRb and bRc together force aRc. "Is an ancestor of" is transitive; "is a friend of" is not. A single broken chain breaks the property: {(1,2),(2,3)} is not transitive because (1,3) is missing.
Antisymmetric — two-way ties force equality
R is antisymmetric if aRb and bRa together force a=b. The order relation ≤ is antisymmetric: a≤b and b≤a give a=b. It does not ban self-pairs like (1,1); it only rules out distinct elements related both ways.
Test the properties in order of ease — reflexivity first, then symmetry, transitivity. A single counterexample is enough to disprove any of them.
| Property | Condition |
|---|---|
| Reflexive | ∀a, aRa |
The relation less than from A to B collects every ordered pair whose first element, taken from A, is smaller than its second, taken from B, tested pair by pair. Reversing the roles of the two sets turns less than into its converse, greater than. …
List all (a,b) with a∈A, b∈B, a<b: seven pairs. The relation from B to A is its converse, "b is greater than a".
Concept. A relation "less than" from A to B collects ordered pairs (a,b) with a∈A, b∈B and a<b.
Build R (a<b), A={1,2,3,4,5}, B={1,4,5}. Test each b∈B:
- b=1: no a∈A with a<1.
- b=4: a∈{1,2,3}⇒(1,4),(2,4),(3,4).
- b=5: a∈{1,2,3,4}⇒(1,5),(2,5),(3,5),(4,5).
R={(1,4),(2,4),(3,4),(1,5),(2,5),(3,5),(4,5)}.
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Showing the 12 most recent of 41 on this concept.
- CBSE 2026Set V11 markMCQQ.If a relation R in the set {1,2,3} be defined by R={(1,1),(2,2)} then R is(a) symmetric but not transitive(b) transitive but not symmetric(c) symmetric and transitive(d) neither symmetric nor transitive
›Reveal solutionSolution
R={(1,1),(2,2)} is both symmetric and transitive, so the answer is (c).
Symmetry: whenever (a,b)∈R we need (b,a)∈R. Here the only pairs are (1,1) and (2,2), and each is its own reverse, so symmetry holds. …
- CBSE 2026Set A1 markMCQQ.What type of a relation is "less than" in the set of real numbers?(a) Only symmetric(b) Only transitive(c) Only reflexive(d) Equivalence
›Reveal solutionSolution
"<" on R is transitive only.
Consider the relation "a<b" on R:
- Reflexive? a<a is false for every a, so NOT reflexive.
- Symmetric? a<b does not imply b<a, so NOT symmetric. …
- CBSE 2026Set ANNUAL1 markMCQQ.If R is the relation {(1,1),(2,2),(3,3),(1,2),(2,3),(1,3)} on A={1,2,3}, then which one of the following is true for R?(a) Reflexive but not symmetric(b) Reflexive but not transitive(c) Symmetric and transitive(d) Neither symmetric nor transitive
›Reveal solutionSolution
R is reflexive (it contains every (x,x)) but not symmetric, since (1,2)∈R while (2,1)∈/R.
Given: R={(1,1),(2,2),(3,3),(1,2),(2,3),(1,3)} on A={1,2,3}.
Reflexivity: R is reflexive if (x,x)∈R for every x∈A. Here (1,1),(2,2),(3,3) are all present, so R is reflexive.
Symmetry: R is symmetric if (x,y)∈R⇒(y,x)∈R. Here (1,2)∈R but (2,1)∈/R. So R is not symmetric.
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- CBSE 2026Set ANNUAL1 markMCQQ.Let R be the relation in the set N given by R={(a,b):a=b−2,b>6}, choose the correct answer:(a) (2,4)∈R(b) (3,8)∈R(c) (6,8)∈R(d) (8,6)∈R
›Reveal solutionSolution
Check each pair against both conditions a=b−2 and b>6.
R={(a,b):a=b−2, b>6}
- (2,4): a=b−2⇒2=2 ✓, but b>6⇒4>6 ✗. Not in R.
- (3,8): a=b−2⇒3=6 ✗. Not in R. …
- CBSE 2026Set ANNUAL1 markMCQQ.Choose the correct answer : Let R be a relation in the set {1,2,3,4} given by R={(1,2),(2,2),(1,1),(4,4),(1,3),(3,3),(3,2)}. Then(a) R is reflexive and symmetric but not transitive(b) R is reflexive and transitive but not symmetric(c) R is symmetric and transitive but not reflexive(d) R is an equivalence relation
›Reveal solutionSolution
Test R against the three defining properties (reflexive, symmetric, transitive) one at a time, directly from its listed ordered pairs.
R={(1,2),(2,2),(1,1),(4,4),(1,3),(3,3),(3,2)} on {1,2,3,4}.
Reflexive? Need (a,a)∈R for every a∈{1,2,3,4}: (1,1) ✓, (2,2) ✓, (3,3) ✓, (4,4) ✓. All present — R is reflexive.
Symmetric? Need: whenever (a,b)∈R, also (b,a)∈R. Take (1,2)∈R: is (2,1)∈R? It is not in the list. So R is not symmetric.
Transitive? Need: whenever (a,b)∈R and (b,c)∈R, also (a,c)∈R. Checking every chain:
- (1,1),(1,2)⇒(1,2) ✓
- (1,1),(1,3)⇒(1,3) ✓
- (1,2),(2,2)⇒(1,2) ✓
- (1,3),(3,3)⇒(1,3) ✓
- (1,3),(3,2)⇒(1,2) ✓ …
- CBSE 2026Set ANNUAL1 markMCQQ.If R be the relation in the set N given by R={(a,b):a=b−2,b>6}, then(a) (2,4)∈R(b) (3,8)∈R(c) (6,8)∈R(d) (8,7)∈R
›Reveal solutionSolution
Only (6,8) satisfies a=b−2 with b>6.
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- CBSE 2025Set X11 markMCQQ.A relation R in a set A is called Reflexive relation if(a) (a,a)∈R for all a∈A(b) (a,a)∈R for atleast one a∈A(c) (a,b)∈R implies (b,a)∈R(d) (a,b)∈R and (b,c)∈R implies (a,c)∈R
›Reveal solutionSolution
Tests the definition of a reflexive relation — correct option is (a).
A relation R on a set A is reflexive when every element is related to itself. Formally, (a,a)∈R must hold for all a∈A — not just for at least one element. Option (c) states symmetry ((a,b)∈R⇒(b,a)∈R) and option (d) states transitivit …
- CBSE 2025Set IX1 markMCQQ.A relation R={(a,b):a=b−1, b≥3} is defined on set N, then(a) (2,4)∈R(b) (4,5)∈R(c) (4,6)∈R(d) (1,3)∈R
›Reveal solutionSolution
Only (4,5) satisfies a=b−1 with b≥3; option (b).
Concept. A pair (a,b) belongs to R only if it satisfies both conditions: a=b−1 and b≥3.
- (2,4): b−1=3=2. ✗ …
- CBSE 2025Set ANNUAL1 markMCQQ.If A={1,2,3,4} and R={(a,b)∣a+b is an odd number, a,b∈A} is a relation from A to A, then which of the following is true for the relation R?(i) Reflexive(ii) Symmetric(iii) Transitive(iv) Equivalent
›Reveal solutionSolution
Check each property directly: R turns out to be symmetric only.
A={1,2,3,4}, R={(a,b):a+b is odd}.
Reflexive? (a,a) needs a+a=2a to be odd — but 2a is always even. So R is not reflexive.
Symmetric? If a+b is odd, then b+a=a+b is the same sum, also odd. So (a,b)∈R⇒(b,a)∈R. R is symmetric.
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- CBSE 2025Set ANNUAL1 markMCQQ.Let A={a,b,c} and R={(a,a),(a,b),(b,a)}, then R is(a) reflexive and symmetric but not transitive(b) reflexive and transitive but not symmetric(c) symmetric and transitive but not reflexive(d) an equivalence relation
›Reveal solutionSolution
R is symmetric (the only cross-pair (a,b)/(b,a) both appear) and not transitive ((b,a) & (a,b) would force (b,b), which is missing) — matching option (a) once we note a reflexivity caveat below.
Step 1 — Reflexive? Full reflexivity on A = {a, b, c} needs (a,a), (b,b), (c,c) all in R. Only (a,a) is present; (b,b) and (c,c) are not. So strictly, R is not fully reflexive on {a,b,c}.
Step 2 — Symmetric? The only pair with a 'partner' is (a,b), and its reverse (b,a) is also in R. There is no pair in R whose reverse is missing. So R is symmetric.
Step 3 — Transitive? Take (b,a) ∈ R and (a,b) ∈ R: transitivity would require (b,b) ∈ R. It is not. So R is not transitive.
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- CBSE 2025Set ANNUAL1 markMCQQ.Relation R = {(x, y) : x < y² where x, y ∈ R} is:(a) Reflexive but not symmetric.(b) Symmetric and transitive but not Reflexive.(c) Reflexive and Symmetric.(d) Neither reflexive nor symmetric nor transitive.
›Reveal solutionSolution
Test each property of R={(x,y):x<y2} with concrete counterexamples — all three fail.
Reflexive? Need x<x2 for every x∈R. Take x=21: is 21<41? No. So R is not reflexive.
Symmetric? Need x<y2⇒y<x2. Take x=0,y=1: 0<12 is true, so (0,1)∈R. But is 1<02=0? No. So (1,0)∈/R, and R is not symmetric.
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- CBSE 2025Set ANNUAL1 markMCQQ.The relation R = {(a, a), (b, b), (c, c)} on the set A = {a, b, c} is ...........(a) Identity(b) Reflexive only(c) Symmetric only(d) Equivalence
›Reveal solutionSolution
R = {(a,a), (b,b), (c,c)} is reflexive, symmetric, and transitive on A = {a, b, c}, so by definition it is an equivalence relation (it is in fact the identity relation, which is always the smallest possible equivalence relation on a set).
Check reflexive: For every element x∈A, (x,x)∈R. Indeed (a,a),(b,b),(c,c) are all present. So R is reflexive.
Check symmetric: If (x,y)∈R then (y,x)∈R. Since every pair here has x=y, this holds trivially.
Check transitive: If (x,y)∈R and (y,z)∈R then (x,z)∈R. Again since all pairs are of the form (x,x), this holds trivially.
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