Class 12th

Contributor-Level 10

This is a assertion and reason answer type question as classified in NCERT Exemplar

Correct option is (iii)

HNO₃ forms an oxide layer on the surface of iron. This is also known as corrosion or rusting.

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7 months ago

Let $f : R \to R$ be the function defined by $f (x) = \frac{1}{2 - c o s x}, \forall x \in R$ . Then, find the range of $f$ .

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

Contributor-Level 10

This is a Short Answer Type Question as classified in NCERT Exemplar

Sol:

$\begin{array}{l} f (x) \frac{1}{2 - c o s x}, \forall x \in R \\ R a n g e o f c o s x i s [- 1, 1] \\ L e t f (x) = y = \frac{1}{2 - c o s x} \\ \Rightarrow 2 y - y c o s x = 1 \Rightarrow y c o s x = 2 y - 1 \\ \Rightarrow c o s x = \frac{2 y - 1}{y} = 2 - \frac{1}{y} \\ N o w - 1 \leq c o s x \leq 1 \\ \Rightarrow - 1 \leq 2 - \frac{1}{y} \leq 1 \Rightarrow - 1 - 2 \leq - \frac{1}{y} \leq 1 - 2 \\ \Rightarrow - 3 \leq - \frac{1}{y} \leq - 1 \Rightarrow 3 \geq \frac{1}{y} \geq 1 \Rightarrow \frac{1}{3} \leq y \leq 1 \\ ∴ t h e r a n g e o f f = [\frac{1}{3}, 1] . \end{array}$

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7 months ago

In the following questions a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.

Assertion : N₂ is less reactive than P₄.

Reason : Nitrogen has more electron gain enthalpy than phosphorus.

(i) Both assertion and reason are correct statements, and reason is the correct explanation of the assertion.

(ii) Both assertion and reason are correct statements, but reason is not the correct explanation of the assertion.

(iii) Assertion is correct, but reason is wrong statement.

(iv) Assertion is wrong but reason is correct statement.

(v) Both

...more

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Contributor-Level 10

This is a assertion and reason answer type question as classified in NCERT Exemplar

Correct option is (iii)

Nitrogen gas has a complete octet structure for both atoms and is unreactive due to the presence of a strong triple bond. On the other hand, phosphor has bonds with unstable angles strains compared to nitrogen, therefore it burns quickly, thus readily reacts. Nitrogen has a lower electron gain enthalpy than phosphorus.

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7 months ago

If functions $f : A \to B$ and $g : B \to A$ satisfy $g ? f = I_{A}$ , then show that $f$ is one-one and $g$ is onto.

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

Contributor-Level 10

This is a Short Answer Type Question as classified in NCERT Exemplar

Sol:

$\begin{array}{l} \end{array} L e t x_{1}, x_{2} \in g o f$

$g o f {f (x_{1})} = g o f {f (x_{2})}$

$\Rightarrow g (x_{1}) = g (x_{2}) \begin{array}{l} \end{array}$

$∴$
$\begin{array}{l} x_{1} = x_{2} \end{array}$

$\begin{array}{l} H e n c e, f i s o n e - o n e a n d g i s o n t o . \end{array}$

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7 months ago

Which of the following statements are true?

(i) Only type of interactions between particles of noble gases are due to weak dispersion forces.

(ii) Ionisation enthalpy of molecular oxygen is very close to that of xenon.

(iii) Hydrolysis of XeF₆ is a redox reaction.

(iv) Xenon fluorides are not reactive.

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Class 12th Dual Nature of Radiation and Matter

Contributor-Level 10

This is a multiple choice answer as classified in NCERT Exemplar

Correct option is (i) and (ii)

(i) The modest dispersion force causes attraction in noble gases.

(ii) In nature, xenon fluorides are reactive.

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7 months ago

A neutron beam of energy E scatters from atoms on a surface with a spacing d = 0.1 nm. The first maximum intensity in the reflected beam occurs at θ= 30°. What is the kinetic energy E of the beam in eV?

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Pallavi Pathak

Contributor-Level 10

Explanation- given d= 0.1nm, $?$ =30⁰ and n=1

According to bragg's law

2dsin $?$ = n $?$

2 $* 0.1 * s i n 30 = ?$

$? = 0.1 n m = 10^{- 10}$

$? = \frac{h}{m v} = \frac{h}{p}$

P=h/ $?$ = $\frac{6.62 * 10^{- 34}}{10^{- 10}}$ = 6.62 $* 10^{- 24}$ kgm/s

k.E= 1/2mv²= $\frac{1}{2} \frac{m^{2} v^{2}}{m}$ = $\frac{p^{2}}{2 m}$ = 0.21eV

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7 months ago

Let $X = {1, 2, 3}$ and $Y = {4, 5}$ . Find whether the following subsets of $X * Y$ are functions from $X$ to $Y$ or not:

$I. f = {(1, 4), (1, 5), (2, 4), (3, 5)}$

$II. g = {(1, 4), (2, 4), (3, 4)}$

$III. h = {(1, 4), (2, 5), (3, 5)}$

$IV. k = {(1, 4), (2, 5)}$ .

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

Contributor-Level 10

This is a Short Answer Type Question as classified in NCERT Exemplar

Sol:

$G i v e n t h a t,$

$\begin{array}{l} X = {1, 2, 3} a n d Y = {4, 5} \end{array}$

$\begin{array}{l} ∴ X * ? Y = {(1, 4), (1, 5), (2, 4), (2, 5), (3, 4), (3, 5)} \end{array}$

$\begin{array}{l} (i) f = {(1, 4), (1, 5), (2, 4), (3, 5)} \end{array}$

$\begin{array}{l} f i s n o t a f u n c t i o n b e c a u s e f h a s n o u n i q u e i m a g e . \end{array}$

$\begin{array}{l} (i i) g = {(1, 4), (2, 4), (3, 4)} \end{array}$

$\begin{array}{l} S i n c e, g i s a f u n c t i o n a s e a c h e l e m e n t o f t h e d o m a i n h a s a u n i q u e i m a g e . \end{array}$

$\begin{array}{l} (i i i) h = {(1, 4), (2, 5), (3, 5)} \end{array}$

$\begin{array}{l} I t i s a f u n c t i o n a s e a c h e l e m e n t o f t h e d o m a i n h a s a u n i q u e i m a g e . \end{array}$

$\begin{array}{l} (i v) k = {(1, 4), (2, 5)} \end{array}$

$\begin{array}{l} k i s n o t a f u n c t i o n a s 3 d o e s n o t h a v e a n y i m a g e u n d e r t h e m a p p i n g . \end{array}$

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7 months ago

In which of the following reactions conc. H₂SO₄ is used as an oxidising reagent?

(i) CaF₂ + H₂SO₄ →CaSO₄ + 2HF

(ii) 2HI + H₂SO4 → I₂ + SO₂ + 2H₂O

(iii) Cu + 2H₂SO₄ →CuSO₄ + SO₂ + 2H₂O

(iv) NaCl + H₂SO₄ → NaHSO₄+ HCl

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Contributor-Level 10

This is a multiple choice answer as classified in NCERT Exemplar

Correct option is (ii) and (iii)

Here fig (b) contains one S-S bond.

The oxidising behaviour of H₂SO₄is represented by (ii) and (iii) among the aforementioned four. It oxidises HI in reaction (ii) and then reduces to SO₂.

The oxidation state of sulphur's core atom drops from +6 to +4. It oxidises copper in (iii) and is reduced to SO₂.

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7 months ago

Let the function $f : R \to R$ be defined by $f (x) = c o s x, \forall x \in R .$ Show that $f$ is neither one-one nor onto.

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

Contributor-Level 10

This is a Short Answer Type Question as classified in NCERT Exemplar

Sol:

$\begin{array}{l} G i v e n f u n c t i o n, f (x) = c o s x \forall x \in R \\ L e t [- \frac{π}{2}, \frac{π}{2}] \in f (x) \\ f (- \frac{π}{2}) = c o s (- \frac{π}{2}) = c o s \frac{π}{2} = 0 \\ c o s (\frac{π}{2}) = c o s \frac{π}{2} = 0 \\ B u t - \frac{π}{2} \neq \frac{π}{2} \\ ∴, f (x) i s n o t o n e - o n e . \\ N o w, f (x) = c o s x, \forall x \in R i s n o t o n t o a s t h e r e i s n o p r e - i m a g e f o r a n y r e a l n u m b e r . \\ W h i c h d o e s n o t b e l o n g t o t h e i n t e r v a l s [- 1, 1], t h e r a n g e o f c o s x . \end{array}$

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7 months ago

Which of the following statements are correct?

(i) S–S bond is present in H₂S₂O₆.

(ii) In peroxosulphuric acid H₂SO₄ sulphur is in +6 oxidation state.

(iii) Iron powder along with Al₂O₃ and K₂O is used as a catalyst in the preparation of NH₃ by Haber's process.

(iv) Change in enthalpy is positive for the preparation of SO₃ by catalytic oxidation of SO₂.

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