The value of $A \cup \phi$ is: (a) 0 (b) A (c) $\phi$ (d) $A\phi$

The value of A ∪ φ is: (a) 0 (b) A (c) φ (d) Aφ

Question of 132

A \cup \phi

(a) 0

(b) A

(c)

\phi

(d)

A\phi

Madhya Pradesh MpbseMP Board Higher Secondary (Class 11) 2024MCQ· 1mImportance★★★★★

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Concept understanding — Set Operations

The idea in plain words

Think of your two favourite groups of friends — the ones who play cricket and the ones who play football. Some friends are in both groups, some in only one, and some in neither. Set operations are simply the mathematical ways to answer questions like: "Who's in at least one team?" or "Who's only in the cricket team?".

The whole secret? Each operation is just a different way of combining or comparing two collections — like sorting your friends into different buckets.

Why this works

Sets are just labelled buckets that hold distinct items. The universal set $U$ is the "whole world" of things we're talking about — say, all your friends. Then each operation picks out a specific bucket:

Operation	What it asks	Bucket contains
Union ( $A \cup B$ )	In either?	Everything from $A$ or $B$ (or both)
Intersection ( $A \cap B$ )	In both?	Only the overlap
Difference ( $A \setminus B$ )	In $A$ but not $B$ ?	Just the part of $A$ that doesn't touch $B$
Complement ( $A^c$ )	Not in $A$ ?	Everything outside $A$ (inside $U$ )
Symmetric Difference ( $A \triangle B$ )	In exactly one?	The two crescent-shaped parts, excluding the overlap

Step by step

Let's take two concrete sets so you can see each operation in action:

A = \{1, 2, 3\}, \quad B = \{3, 4, 5\}

Step 1: Union — gather everything from both, but don't repeat anything.

A \cup B = \{1, 2, 3, 4, 5\}

Step 2: Intersection — only what's common to both.

A \cap B = \{3\}

Step 3: Difference ( $A$ minus $B$ ) — start with $A$ , remove anything that's also in $B$ .

A \setminus B = \{1, 2\}

Step 4: Complement — needs a universal set. Let $U = \{1, 2, 3, 4, 5\}$ . Then:

A^c = \{4, 5\}

Step 5: Symmetric Difference — combine the two differences:

A \triangle B = (A \setminus B) \cup (B \setminus A) = \{1, 2\} \cup \{4, 5\} = \{1, 2, 4, 5\}

A common slip …

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$\phi$ is the identity element for set union, so $A \cup \phi = A$ .

Step 1. $A \cup \phi$ is the set of all elements in $A$ or in $\phi$ .

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Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

Showing the 12 most recent of 52 on this concept.

CBSE 2026Set ANNUAL1 markMCQ
$Q. The shaded region in the given Venn-diagram represents:$
(a) A ∪ B
(b) A ∩ B
(c) (A ∪ B)'
(d) (A ∩ B)'
›Reveal solutionSolution

The shaded region is everything in the universal set except A and B combined, which is exactly $(A \cup B)'$ .

The rectangle is the universal set $U$ , and the two overlapping circles are sets $A$ and $B$ . The description tells us the shading covers the rectangle except the two circles — i.e. every point that lies outside both $A$ and $B$ .

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CBSE 2026Set ANNUAL1 mark
$Q. If U = {1, 2, 3, 4, 5, 6, 7, 8, 9}, A = {2, 4, 6, 8} and B = {2, 3, 6, 7}, then (A \cup B)' = ..............$
›Reveal solutionSolution

Find A∪B first, then take its complement in U.

Given $U=\{1,2,3,4,5,6,7,8,9\}$ , $A=\{2,4,6,8\}$ , $B=\{2,3,6,7\}$ .

First find $A\cup B$ (all elements in A or B or both):

$A\cup B = \{2,3,4,6,7,8\}$

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CBSE 2026Set ANNUAL1 markMCQ
$X = \{1, 3, 5\}$
(a) $\{1, 2, 3, 4, 5\}$
(b) $\{1, 2, 3, 5\}$
(c) $\{1, 3\}$
(d) $\phi$
›Reveal solutionSolution

$X \cap Y$ consists of elements present in both $X$ and $Y$ , which gives $\{1,3\}$ .

Given $X = \{1,3,5\}$ and $Y=\{1,2,3\}$ . The intersection $X \cap Y$ contains only those elements that belong to BOTH sets.

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CBSE 2026Set ANNUAL1 mark
$\{2, 6, 10\}$
›Reveal solutionSolution

Sets are disjoint when their intersection is empty; comparing the elements of $\{2,6,10\}$ and $\{3,7,11\}$ shows no overlap.

Set $A=\{2,6,10\}$ and set $B=\{3,7,11\}$ .

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CBSE 2025Set ANNUAL1 markMCQ
$A = \{1, 2, 3\}, B = \{2, 3, 7\} \Rightarrow A \cup B =$
(a) $\{1, 2, 3\}$
(b) $\{1, 3, 7\}$
(c) $\{1, 2, 3, 7\}$
(d) $\{1, 2, 7\}$
›Reveal solutionSolution

$A \cup B = \{1, 2, 3, 7\}$ : the union lists every element that is in $A$ or in $B$ (or both), each written once.

For sets $A$ and $B$ , the union is $A \cup B = \{x : x \in A \text{ or } x \in B\}$ — combine both sets and remove duplicate entries.

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CBSE 2025Set ANNUAL1 markMCQ
$X = \{3, 5, 7\}, Y = \{2, 3, 5\} \Rightarrow X \cap Y =$
(a) $\{3, 2\}$
(b) $\{3, 7\}$
(c) $\{5, 7\}$
(d) $\{3, 5\}$
›Reveal solutionSolution

$X \cap Y = \{3, 5\}$ : the intersection keeps only elements that belong to both sets.

For sets $X$ and $Y$ , $X \cap Y = \{x : x \in X \text{ and } x \in Y\}$ .

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CBSE 2025Set ANNUAL1 markMCQ
$X = \{1, 2\}, Y = \{2, 3, 5\}, Z = \{4, 6\} \Rightarrow X \cup Y \cup Z =$
(a) $\{1, 2, 3, 5, 6\}$
(b) $\{2, 3, 4, 5, 6\}$
(c) $\{1, 2, 3, 4, 5, 6\}$
(d) $\{1, 2\}$
›Reveal solutionSolution

$X \cup Y \cup Z = \{1, 2, 3, 4, 5, 6\}$ : list every element appearing in at least one of the three sets, once each.

Given $X = \{1, 2\}$ , $Y = \{2, 3, 5\}$ , $Z = \{4, 6\}$ .

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CBSE 2025Set ANNUAL1 markMCQ
$X = \{1, 2, 3, 6\}, Y = \{4, 5, 6\}, Z = \{4, 2, 3, 6\} \Rightarrow (X \cup Y) \cap Z =$
(a) $\{2, 3, 4, 6\}$
(b) $\{1, 5\}$
(c) $\{1, 2, 5\}$
(d) $\{1, 2, 3, 5\}$
›Reveal solutionSolution

$(X \cup Y) \cap Z = \{2, 3, 4, 6\}$ , found by first taking the union, then intersecting with $Z$ .

Given $X = \{1, 2, 3, 6\}$ , $Y = \{4, 5, 6\}$ , $Z = \{4, 2, 3, 6\}$ .

Step 1: $X \cup Y = \{1, 2, 3, 4, 5, 6\}$ (combine both, 6 counted once).

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CBSE 2025Set ANNUAL1 markMCQ
$X = \{a, b, c, d\}, Y = \{c, a, r\}, Z = \{r, o, b\} \Rightarrow (X \cap Y) \cup Z =$
(a) $\{a, b, c, o, r\}$
(b) $\{c, a, r, b\}$
(c) $\{r, o, b, c\}$
(d) $\phi$
›Reveal solutionSolution

$(X \cap Y) \cup Z = \{a, b, c, o, r\}$ , found by first taking the intersection, then the union with $Z$ .

Given $X = \{a, b, c, d\}$ , $Y = \{c, a, r\}$ , $Z = \{r, o, b\}$ .

…

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CBSE 2025Set ANNUAL1 markMCQ
$A = \{x : x - 2 = 0\}, B = \{x : 2x = 6\} \Rightarrow A \cup B =$
(a) $\{2, 6\}$
(b) $\{-2, 6\}$
(c) $\{2, 3\}$
(d) $\{2, -3\}$
›Reveal solutionSolution

$A \cup B = \{2, 3\}$ .

$A = \{x : x - 2 = 0\} = \{2\}$ . $B = \{x : 2x = 6\} = \{3\}$ .

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CBSE 2025Set ANNUAL1 markMCQ
$A = \{x : x^2 + 5x + 6 = 0\}, B = \{x : x^2 + 8x + 15 = 0\} \Rightarrow$
(a) $A \subset B$
(b) $B \subset A$
(c) $A = B$
(d) $A \cap B = \{-3\}$
›Reveal solutionSolution

$A = \{-2, -3\}$ , $B = \{-3, -5\}$ , and their only common element is $-3$ , so $A \cap B = \{-3\}$ .

$A = \{x : x^2 + 5x + 6 = 0\}$ : factorising, $(x+2)(x+3) = 0 \Rightarrow x = -2, -3$ , so $A = \{-2, -3\}$ .

$B = \{x : x^2 + 8x + 15 = 0\}$ : factorising, $(x+3)(x+5) = 0 \Rightarrow x = -3, -5$ , so $B = \{-3, -5\}$ .

…

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CBSE 2025Set ANNUAL1 markMCQ
$U = \{1, 2, \ldots, 15\}$
(a) $\{4, 6, 7, 8, 9, 10, 11, 12, 13, 14\}$
(b) $\{4, 6, 8, 10, 12, 14\}$
(c) $\{8, 10, 12, 14\}$
(d) $\phi$
›Reveal solutionSolution

$A' = U - A = \{4, 6, 7, 8, 9, 10, 11, 12, 13, 14\}$ .

Given $U = \{1, 2, \ldots, 15\}$ and $A = \{1, 2, 3, 5, 15\}$ . The complement $A' = U - A$ consists of every element of $U$ not in $A$ .

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Q.The value of A∪ϕA \cup \phiA∪ϕ is:

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Q.The value of $A \cup \phi$ is:

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