Chemistry: Solved Previous Year’s Question Paper for NCERT/CBSE Class 12th Chemistry Paper Code (HSEIIRKO-13-X)

Chemistry: Solved Previous Year’s Question Paper for NCERT/CBSE Class 12th Chemistry Paper Code (HSEIIRKO-13-X)

Long Answer Type Questions (Each carries 5 Marks)

Question: Discuss briefly the oxidation states of the 3d-transition series.

Answer: The 3d-transition series is composed of elements from the fourth period of the periodic table, including scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu).

The oxidation states of these elements range from -2 to +8. Sc and Ti have the widest range of oxidation states, ranging from -2 to +7, while V, Cr, and Mn typically have oxidation states ranging from -2 to +6. Fe, Co, and Ni typically have oxidation states of -2, +2, +3, and +4, and Cu typically has oxidation states of +1 and +2.

Question: What are co-ordination isomers? Explain with suitable Examples.

Answer: Co-ordination isomers are compounds which have the same molecular formula but different structural isomerism due to the arrangement of ligands around the central atom. They differ from stereoisomers in that the arrangement of atoms in space is the same, but the arrangement of ligands around the central atom is different. An example of co-ordination isomers is the isomerism exhibited by nickel complexes, such as the hexaamminecobalt (III) chloride and hexaamminecobalt (III) bromide. Both complexes have the same chemical formula, [Co(NH3)6]Cl3 and [Co(NH3)6]Br3, but different structural arrangements of the ligands around the central cobalt atom.

Question: Name oxides of Nitrogen. What is the nature of these oxides? Give their structure.

Answer: The oxides of nitrogen are nitrogen monoxide (NO) and nitrogen dioxide (NO2).

Nitrogen monoxide is a colourless, odourless gas with a molecular formula of NO. It exists as a diatomic molecule, with the structure of two N-O single bonds.


Nitric oxide is a linear molecule. The bond length between nitrogen and oxygen is 115pm. It forms two resonating structures

 Nitrogen dioxide is a red-brown gas with a molecular formula of NO2. Its structure consists of two double bonds between the two nitrogen atoms and two oxygen atoms, with each oxygen atom having a single lone pair. It is a strong oxidizing agent and is highly reactive.


Nitrogen dioxide has a bent shape. The N-O is 120pm long. The angle between is 134o

Short Answer Type Questions (Each carry 3 Marks)

Question: What is electrolytic conductance? How is it measured experimentally? Give S.I.Units.

Answer: Electrolytic conductance is the measure of a liquid’s ability to conduct electricity. It is measured experimentally by passing an electric current through the liquid and measuring the electrical resistance. The SI unit for electrolytic conductance is Siemens (S).

Question: Write the structure of Pyrophosphoric acid.

Answer: Pyrophosphoric acid (H4P2O7) is a polyprotic acid composed of four hydrogen atoms, two phosphorus atoms, and seven oxygen atoms. Its molecular formula is H4P2O7.

Question: Differentiate Lycophillic collides from Lymphobic colloids.

Answer: 1. Lycophillic colloids are colloids that have an affinity for water, meaning they will dissolve in water.

2. They are generally composed of small molecules or particles that can be suspended in a liquid medium.

3. Examples include proteins, enzymes, and some polymers.

1. Lymphobic colloids are colloids that are not soluble in water but may be soluble in other solvents, such as alcohol or organic solvents.

2. They are generally composed of larger molecules or particles that cannot be suspended in a liquid medium.

3. Examples include waxes, fats, oils, and some polymers.

Question: What are P-block elements? Briefly discuss their magnetic behaviour.

Answer: P-block elements are a group of elements located in the periodic table in the p-block section, which includes the elements in groups 13-18. These elements have a wide variety of characteristics, but they all have four electrons in their outermost shell, which allows them to form strong bonds with other elements.

The magnetic behaviour of P-block elements depends on the number of unpaired electrons in their outermost shell. If there are an odd number of unpaired electrons, the element is paramagnetic and will be attracted to an externally applied magnetic field. If there are an even number of unpaired electrons, the element is diamagnetic and will be repelled by an externally applied magnetic field.

Question: What are Hydrate isomers? Explain with suitable examples.

Answer: Hydrate isomers are different compounds that have the same molecular formula but different structural formulas. They are formed when the same molecules contain different numbers of water molecules. Examples of hydrate isomers include sodium chloride (NaCl) and sodium chloride hexahydrate (NaCl·6H2O). The first compound is a white crystalline solid, while the second is a colourless crystalline powder.

Question: Give one example of Ferrimagnetic substances.

Answer: Ferrimagnetic substances include magnetite (Fe3O4), lodestone (Fe3C), and pyrrhotite (Fe1-xS).

Question: What are Nitriles and Isonitriles? Give one method of preparation of Nitriles.

Answer: Nitriles and Isonitriles are organic compounds that contain a cyano group, -C≡N, attached to a carbon atom. Nitriles contain a triple bond between the carbon and nitrogen atoms, while Isonitriles contain a single bond.

One method of preparing nitriles is through the reaction between an organic halide and silver cyanide. This reaction is known as the “Friedel-Crafts acylation” and produces nitrile as the product.

The reaction proceeds as follows: R-X + AgCN → R-CN + AgX.

For example, you will get ethanenitrile by dehydrating ethanamide

Objective Type Questions (Each carries 1 Marks)

 (i) The speed of any chemical reaction is directly proportional to the molar concentration (True/False)

Answer: True

(ii) The boiling point of halo-alkanes are in the order

Answer: 1. Methane (CH4) 2. Ethane (C2H6) 3. Propane (C3H8) 4. Butane (C4H10) 5. Pentane (C5H12) 6. Hexane (C6H14) 7. Heptane (C7H16) 8. Octane (C8H18) 9. Nonane (C9H20) 10. Decane (C10H22)

(iii) Alcohols react with metal hydrides evolve ———-gas

Answer: Hydrogen gas.

(iv) Formaldehyde reacts with Ammonia and gives Hexamethylene tetra—amine (True/False)

Answer: True

(v) Name the chemical substance which acts as an antiseptic as well as disinfectant

Answer: Chlorhexidine

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