JKBOSE Chemistry: Solved Previous Year’s Question Paper for NCERT/CBSE  Class 12th Chemistry Paper Code (HSEIIRKO-45018–B)

JKBOSE Chemistry: Solved Previous Year’s Question Paper for NCERT/CBSE  Class 12th Chemistry Paper Code (HSEIIRKO-45018–B)

Long Answer Type Questions (Each carries 5 Marks)

Question: Define Allotropy. Explain different allotropic forms of Phosphorus.

Answer: Allotropism is the physical property of some chemical elements to exist in two or more different forms, known as allotropes of the elements. e.g. the form of the elements carbon or phosphorus.

The allotropic forms of phosphorus are white phosphorus, red phosphorus, and black phosphorus.

White phosphorus is the most common form of phosphorus and is a waxy, white or transparent solid. It is highly reactive and is considered to be the most dangerous form of phosphorus, as it is highly flammable and toxic.

Red phosphorus is a non-flammable, reddish-brown solid. It is less reactive than white phosphorus and is much safer to handle.

Black phosphorus is a black, crystalline solid which is more stable than white phosphorus. It is more difficult to ignite and less toxic than white phosphorus.

Question: How is Ozone prepared? Give its three oxidizing properties

Answer: Ozone is prepared by passing a silent electric discharge through dry air.

                    O2  O + O

                     O2 + O O3

 Its three oxidizing properties are as follows:

1. Ozone is a strong oxidizing agent and can oxidize a wide range of organic and inorganic compounds.

2. Ozone is soluble in water and can dissolve in it.

3. Ozone has a higher oxidation potential than oxygen and can be used to generate free radicals and other reactive oxygen species.

Question: Discuss How H2SO4 manufactured by contact process.

Answer: Sulfuric acid (H2SO4) is manufactured by the contact process.

This process involves the following steps:

1. Sulfur dioxide is produced by burning sulfur in the presence of air.

2. The sulfur dioxide is then passed through a catalyst containing vanadium pentoxide, which converts it to sulfur trioxide.

3. The sulfur trioxide is then dissolved in concentrated sulfuric acid to form oleum.

4. The oleum is then passed through a catalyst containing platinum which oxidizes it to sulfuric acid.

5. The sulfuric acid is then cooled and treated with water to produce the desired concentration of H2SO4.

The contact process is the most efficient and cost-effective way of producing sulfuric acid and is used in large-scale industrial operations.

Question: How K2Cr2O7 is prepared? Give its three oxidizing properties.

Answer: K2Cr2O7 is prepared by reacting solid potassium dichromate (K2Cr2O7) with concentrated sulfuric acid (H2SO4).


The three oxidizing properties of K2Cr2O7 are:

1. It oxidizes sulfur dioxide (SO2) to sulfur trioxide (SO3).

2. It oxidizes carbon monoxide (CO) to carbon dioxide (CO2).

3. It oxidizes alcohols to aldehydes or ketones.

Question:  Give five chemical properties of Carboxylic acids.

Answer: 1. Carboxylic acids have a sour taste.

2. Carboxylic acids are strong electrolytes, meaning they easily dissociate in water.

3. Carboxylic acids have higher boiling points than alcohols of similar molecular weight.

4. Carboxylic acids are weak acids, meaning they are partially ionized in solution.

5. Carboxylic acids are soluble in organic solvents such as ethers and acetone.

Short Answer Type Questions (Each carry 3 Marks)

Question: How corrosion is prevented?

Answer: Corrosion can be prevented through a variety of methods. The most common methods include the use of protective coatings such as paint, galvanizing, and anodizing. These coatings act as a barrier between the surface of the metal and the environment, limiting the exposure of the metal to corrosive elements. Additionally, cathodic protection, which uses a sacrificial anode to protect the metal, and inhibitors, which are chemical compounds that slow down the corrosion process, can also be used.

Question:  Explain Ozone refining?

Answer: Ozone refining is a process used to purify and refine petroleum products, such as gasoline and diesel fuel, through the use of ozone gas.

Question:  Give preparation and uses of Polythene.


Preparation of polythene involves a process called polymerization, in which small molecules of ethylene are linked together to form a polymer chain. This is done by passing ethylene gas through a catalyst at a high temperature.The polymer chains then grow by linking together to form a long, repeating chain

Polythene is a type of plastic that is commonly used in many everyday products.

Uses of polythene include packaging, food and beverage containers, toys, furniture, clothing, insulation, and medical devices. It is also used in the manufacturing of plastic bags and films, as well as a variety of other products such as pipes and automotive parts. Polythene is also used in construction and civil engineering projects as a waterproofing material.

Question:  Give three chemical properties of HCL.

Answer: 1) HCl is a strong acid, with a pKa of -6.3.

2) It has a boiling point of -85.6 °C and a melting point of -114.1 °C.

3) HCl is highly soluble in water, with a solubility of 36.5 g/L at 20 °C.

Very Short Answer Type Questions (Each carry 2 Marks)

Question:  State Faraday’s second law of Electrolysis.

Answer: Faraday’s second law of electrolysis states that the mass of a substance altered at an electrode during electrolysis is directly proportional to the quantity of electric charge, or coulombs, passed through the electrolyte solution.

Question:  Why phenols are acidic

Answer: Phenols are acidic in nature because they contain an electrically charged group of atoms called a hydroxyl group (–OH). This group can easily donate a proton (H+) when exposed to a base, making the molecule more acidic.

Question:  Give two chemical properties of ethers.

Answer: 1. Ethers are relatively unreactive and have low boiling points.

2. Ethers are colorless, sweet-smelling, extremely volatile, and combustible liquids.

Question:  Name two Antihistamines

Answer: The two most common antihistamines are cetirizine (Zyrtec) and loratadine (Claritin).

Objective Type Questions (Each carries 1 Marks)

(i) The Insulators have —————- Conductivity

Answer: low

(ii) Two types of Geometric Isomerism in co-ordination compounds are Cis and —————- isomers

Answer: Trans

(iii) The formula of Iodoform is CHBr3. (True/False)

Answer: True

(iv) The chemical which is used to prevent the formation of Acid in thestomach is called as————————

Answer: Antacid.

(v) Write the structure of pentan-2-one



(vi) Write the structure of Glucose and Fructose


(vii) Ethyl amine is ———————

Answer: A tertiary amine

(viii) The Formula of Aniline is ——————-

Answer: C6H5NH2

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