Class 12th

Let $A = {1, 2, 3, \dots, n}$ and $B = {a, b}$ . Then the number of surjections from $A$ into $B$ is

(A) ⁿp₂

(B) $2^{n} - 2$

(C) $2^{n} - 1$

(D) None of these

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Contributor-Level 10

This is a Objective Type Question as classified in NCERT Exemplar

Sol:

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7 months ago

If the set $A$ contains 5 elements and the set $B$ contains 6 elements, then the number of one-one and onto mappings from $A$ to $B$ is

(A) 720

(B) 120

(C) 0

(D) None of these

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Class 12th Chemistry NCERT Exemplar Solutions Class 12th Chapter Seven

Contributor-Level 10

This is a Objective Type Question as classified in NCERT Exemplar

Sol:

$\begin{array}{l} I f A a n d B s e t s h a v e m a n d n e l e m e n t s r e s p e c t i v e l y, \\ t h e n t h e n u m b e r o f o n e - o n e a n d o n t o m a p p i n g f r o m A t o B i s \\ n! i f m = n \\ a n d 0 i f m \neq n \\ H e r e, m = 5 a n d n = 6 \\ 5 \neq 6 \\ S o, N u m b e r o f m a p p i n g = 0 \\ H e n c e, t h e c o r r e c t a n s w e r i s (c) \end{array}$

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7 months ago

Match the items of Columns I and II and mark the correct option.

Code:

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Class 12th Chemistry NCERT Exemplar Solutions Class 12th Chapter Seven

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This is a matching answer type question as classified in NCERT Exemplar

Correct option is (iii)

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7 months ago

Match the species given in Column I with the shape given in Column II and mark the correct option.

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Class 12th Maths NCERT Exemplar Solutions Class 12th Chapter One

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This is a matching answer type question as classified in NCERT Exemplar

Correct option is (ii)

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The identity element for the binary operation $*$ defined on $Q ~ {0}$ as $a * b = \frac{a b}{2} \forall a, b \in Q ~ {0}$ is

(A) 1

(B) 0

(C) 2

(D) None of these

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Class 12th Chemistry NCERT Exemplar Solutions Class 12th Chapter Seven

Contributor-Level 10

This is a Objective Type Question as classified in NCERT Exemplar

Sol:

$\begin{array}{l} G i v e n t h a t : a * b = \frac{a b}{2} \forall a, b \in Q - {0} \\ L e t e b e t h e i d e n t i t y e l e m e n t \\ ∴ a * e = \frac{a e}{2} = a \Rightarrow e = 2 \\ H e n c e, t h e c o r r e c t a n s w e r i s (c) . \end{array}$

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New answer posted

7 months ago

Match the items of Columns I and II and mark the correct option.

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Contributor-Level 10

This is a matching answer type question as classified in NCERT Exemplar

Correct option is (i)

CCl₃NO₂ stands for chloropicrin, which is known as tear gas. Cl is the element of the highest electron gain enthalpy. Sulphur is the element belonging to 16th group, also known as chalcogens.

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7 months ago

Let $A = {1, 2, 3}$ and consider the relation

$R = {(1, 1), (2, 2), (3, 3), (1, 2), (2, 3), (1, 3)}$ .

Then $R$ is

(A) Reflexive but not symmetric

(B) Reflexive but not transitive

(C) Symmetric and transitive

(D) Neither symmetric, nor transitive

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Class 12th Chemistry NCERT Exemplar Solutions Class 12th Chapter Seven

Contributor-Level 10

This is a Objective Type Question as classified in NCERT Exemplar

Sol:

$\begin{array}{l} G i v e n t h a t : A = {1, 2, 3} \\ a n d R = {(1, 1), (2, 2), (3, 3), (1, 2), (2, 3), (1, 3)} \\ H e r e, 1 R 1, 2 R 2 a n d 3 R 3, S o, R i s r e f l e x i v e . \\ 1 R 2 b u t 2 R 1 o r 2 R 3 b u t 3 R 2, \\ S o, R i s n o t s y m m e t r i c . \\ 1 R 1 a n d 1 R 2 \Rightarrow 1 R 3, S o, R i s t r a n s i t i v e . \\ H e n c e, t h e c o r r e c t a n s w e r i s (a) . \end{array}$

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7 months ago

Match the formulas of oxides given in Column I with the type of oxide given in Column II and mark the correct option.

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This is a matching answer type question as classified in NCERT Exemplar

Correct option is (ii)

A. Pb₃O₄is a mixed ore

B. N₂O is a neutral oxide

C. Mn₂O₇is acidic oxide

D. Bi₂O₃is basic oxide

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7 months ago

Let us define a relation $R$ in $R$ as $a R b$ if $a \geq b$ . Then $R$ is:

(A) An equivalence relation

(B) Reflexive, transitive but not symmetric

(C) Symmetric, transitive but not reflexive

(D) Neither transitive nor reflexive but symmetric

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Class 12th Chemistry NCERT Exemplar Solutions Class 12th Chapter Seven

Contributor-Level 10

This is a Objective Type Question as classified in NCERT Exemplar

Sol:

$\begin{array}{l} H e r e, a R b i f a \geq b \\ \Rightarrow a R a \Rightarrow a \geq a w h i c h i s t r u e, s o i t i s r e f l e x i v e . \\ L e t a R b \Rightarrow a \geq b, b u t b \geq a, s o b R a \\ R i s n o t s y m m e t r i c . \\ N o w, a \geq b, b \geq c, \Rightarrow a \geq c, w h i c h i s t r u e . \\ S o, R i s t r a n s i t i v e . \\ H e n c e, c o r r e c t a n s w e r i s (b) . \end{array}$

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New answer posted

7 months ago

Match the compounds given in Column I with the hybridisation and shape given in Column II and mark the correct option

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