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Science (English Medium) Class 12 - CBSE Important Questions

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Write the chemical equations to illustrate the following name reaction: 

Cannizzaro’s reaction

Appears in 10 question papers
Chapter: [8] Aldehydes, Ketones and Carboxylic Acids
Concept: Concepts of Aldehydes, Ketones, and Carboxylic Acids >> Chemical Reactions of Aldehydes and Ketones - Other Reactions

Give reasons for the following:

Aniline does not undergo Friedel- Crafts reaction.

Appears in 10 question papers
Chapter: [9] Amines
Concept: Concept of Amines >> Chemical Reactions of Amines - Electrophilic Substitution

State the two Kirchhoff’s rules used in electric networks. How are there rules justified?

Appears in 10 question papers
Chapter: [3] Current Electricity
Concept: Kirchhoff’s Laws

In a single slit diffraction experiment, the width of the slit is made double the original width. How does this affect the size and intensity of the central diffraction band?

Appears in 10 question papers
Chapter: [10] Wave Optics
Concept: Diffraction of Light >> The Single Slit

Give the truth table and circuit symbol for NAND gate

Appears in 10 question papers
Chapter: [14] Semiconductor Electronics - Materials, Devices and Simple Circuits
Concept: Digital Electronics and Logic Gates

Calculate the freezing point of a solution containing 60 g of glucose (Molar mass = 180 g mol–1) in 250 g of water. (Kf of water = 1.86 K kg mol–1)

Appears in 9 question papers
Chapter: [1] Solutions
Concept: Colligative Properties and Determination of Molar Mass >> Depression of Freezing Point

Give reasons for the following:

Measurement of osmotic pressure method is preferred for the determination of molar masses of macromolecules such as proteins and polymers.

Appears in 9 question papers
Chapter: [1] Solutions
Concept: Colligative Properties and Determination of Molar Mass >> Depression of Freezing Point

Give reasons for the following :

Aquatic animals are more comfortable in the cold water than in warm water.

Appears in 9 question papers
Chapter: [1] Solutions
Concept: Solubility >> Solubility of a Gas in a Liquid

Give reasons for the following

Elevation of the boiling point of 1 M KCl solution is nearly double than that of 1 M sugar solution.

Appears in 9 question papers
Chapter: [1] Solutions
Concept: Abnormal Molar Masses

An element 'X' (At. mass = 40 g mol-1) having f.c.c. the structure has unit cell edge length of 400 pm. Calculate the density of 'X' and the number of unit cells in 4 g of 'X'. (NA = 6.022 × 1023 mol-1)

Appears in 9 question papers
Chapter: [1] Solid State
Concept: Number of Atoms in a Unit Cell

For the reaction

`2AgCl (s) + H_2 (g) ("1 atm") -> 2Ag (s) + 2H^(+)  (0.1 M) +  2Cl^(-) (0.1 M)`

`triangleG^0 = -43600 J at 25^@ C`

Calculate the e.m.f. of the cell

`[log 10^(-n) = -n]` 

Appears in 9 question papers
Chapter: [2] Electrochemistry
Concept: Relation Between Gibbs Energy Change and Emf of a Cell

Write two advantages of fuel cell

Appears in 9 question papers
Chapter: [2] Electrochemistry
Concept: Fuel Cells

An analysis shows that FeO has a non-stoichiometric composition with formula Fe0.95O. Give reason.

Appears in 9 question papers
Chapter: [4] d-block and f-block Elements
Concept: General Properties of the Transition Elements (d-block)

Complete and balance the following chemical equations

`Fe^(2+) + MnO_4^(-) + H^+ ->`

Appears in 9 question papers
Chapter: [4] d-block and f-block Elements
Concept: General Properties of the Transition Elements (d-block)

Complete and balance the following chemical equations

`MnO_4^(-) + H_2O + I^(-) ->`

Appears in 9 question papers
Chapter: [4] d-block and f-block Elements
Concept: General Properties of the Transition Elements (d-block)

Give reasons: 

E° value for the Mn3+/Mn2+ couple is much more positive than that for Fe3+/Fe2+.

Appears in 9 question papers
Chapter: [4] d-block and f-block Elements
Concept: General Properties of the Transition Elements (d-block)

Give reasons Iron has the higher enthalpy of atomization than that of copper.

Appears in 9 question papers
Chapter: [4] d-block and f-block Elements
Concept: General Properties of the Transition Elements (d-block)

Give reasons: Sc3+ is colourless in aqueous solution whereas Ti3+ is coloured.

Appears in 9 question papers
Chapter: [4] d-block and f-block Elements
Concept: General Properties of the Transition Elements (d-block)

Write the formula for the given coordination compound:

Iron (III) hexacyanoferrate (II)

Appears in 9 question papers
Chapter: [5] Coordination Compounds
Concept: Concept of Coordination Compounds

CO (g) and H2 (g) react to give different products in the presence of different catalysts. Which ability of the catalyst is shown by these reactions?

Appears in 9 question papers
Chapter: [5] Surface Chemistry
Concept: Catalysis >> Catalysts in Industry
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