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6 months ago

Class 12th Dual Nature of Radiation and Matter

Given below are two statements : one is labelled as Assertion A and other is labelled as Reason R.

Assertion A : The photoelectric effect does not takes place, if the energy of the incident radiation is less than the work function of a metal.

Reason R : Kinetic energy of the photoelectrons is zero, if the energy of the incident radiation is equal to the work function of a metal.

In the light of the above statements, chose the most appropriate answer from t

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alok kumar singh

Contributor-Level 10

To free the electron from metal surface minimum energy required, is equal to the work function of that metal.

So Assertion A, is correct

have = w₀ + K.E_max

If have = w₀

Þ K.E_max = 0

Hence reas

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6 months ago

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

Which of the following compounds in not aromatic?

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Vishal Baghel

Contributor-Level 10

Both indicated hydrogen atoms repel each other so due steric hinderance the given compound becomes non planar. It is non-aromatic.

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

The elevation in boiling point for 1 molal solution of non-volatile solute A is 3K. The depression in freezing point for 2 molal solution of A in the same solvent is 6 K. The ratio of K_b and K_f i.e. K_b/K_f is 1 : X. The value of X is [nearest integer]

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alok kumar singh

Contributor-Level 10

$Δ T_{b} = i K_{b} m_{1}$

$\frac{Δ T_{b}}{Δ T_{f}} = \frac{K_{b} * 1}{K_{f} * 2} \Rightarrow \frac{3}{6} = \frac{1}{2} = \frac{K_{b}}{k_{f}} * \frac{1}{2}$

$\frac{K_{b}}{K_{f}} = 1 \Rightarrow x = 1$

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6 months ago

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

Which technique among the following is most appropriate in separation of a mixture of 100mg of p-nitrophenol acid and picric acid?

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Vishal Baghel

Contributor-Level 10

Solvent polarity is related to R_f value of nitro compounds

100 mg P-nitrophenol and picric acid have different R_f value on silica gel plate.

Preparative TLC is best to separate 100 mg of P-nitro phenol and picric acid.

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6 months ago

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

For the reaction

H₂F₂(g) ® H₂(g) + F₂(g)

$Δ U = - 59.6 k J m o l^{- 1} a t 27 ° C$

The enthalpy change for the above reaction is ()__________kJ mol^-1. [nearest integer]

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alok kumar singh

Contributor-Level 10

$Δ H = Δ U + Δ n_{g} R T$

$Δ H = - 59.6 + 1 * 8.314 * 300 * 1 0^{- 3} = - 57.10 k J / m o l$

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6 months ago

Class 12th Physics Mechanical Properties of Solids

A wire of length L is hanging from a fixed support. The length changes to L₁ andL₂when masses 1kg and 2kg are suspended respectively from its free end. Then the value of L is equal to:

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alok kumar singh

Contributor-Level 10

Spring constant of wire (k) = $\frac{A E}{L}$

Case 1

$k [Δ] = 1 g$

$k [L_{1} - L] = 1 g$ - (1)

Case 2 $k [L_{2} - L] = 2 g$ - (2)

$(1) \div (2)$

$\frac{L_{1} - L}{L_{2} - L} = \frac{1}{2}$

L = 2L₁ – L₂

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

+ CH₄ --> A + B

A and B in the above atmosphere reaction step are:

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Vishal Baghel

Contributor-Level 10

$\overset{•}{C} l + C H_{3} - H \to \overset{•}{C} H_{3} + H C l$

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

The dark purple colour KMnO₄ disappears in the titration with oxalic acid in acidic medium. The overall change in the oxidation number of manganese in the reaction is:

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Vishal Baghel

Contributor-Level 10

$\overset{+ 7}{M} n O_{4}^{-} + 8 H^{+} + 5 e \to \overset{+ 2}{M} n^{2 +} + 4 H_{2} O$ change in oxidation number of Mn = 7 – 2 = 5

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

Consider an imaginary ion The nucleus contains 'a'% more neutrons that the number f electrons in the ion. The value of 'a' is____________. [nearest integer]