Punjab Chemistry 2018 Paper 2 — Solved MCQs

Question 1

SN2 reactions are best carried by which alkyl halides?

Accepted Answer

A. Primary — Primary alkyl halides are the best substrates for SN2 reactions because they have less steric hindrance around the carbon atom bearing the halogen. This allows the nucleophile to approach the carbon atom from the opposite side of the leaving group with minimal steric hindrance, promoting the SN2 mechanism.

Question 2

Rectified spirit contains alcohol:

Accepted Answer

D. 95% — Rectified spirit typically contains a high concentration of alcohol, usually around 95%. This high concentration makes it suitable for various purposes, including medicinal, industrial, and household uses.

Question 3

Cannizaro's reaction is not given by:

Accepted Answer

B. Acetaldehyde — Acetaldehyde does not undergo Cannizaro's reaction under normal conditions. Instead, it typically undergoes aldol condensation or other types of reactions. Cannizaro's reaction requires the presence of an aldehyde that does not have a hydrogen atom alpha to the carbonyl group (i.e., it does not have a hydrogen atom attached to the carbon adjacent to the carbonyl carbon), which is not the case for acetaldehyde.

Question 4

Which of these is not a fatty acid?

Accepted Answer

C. Phthalic acid — Phthalic acid is not a fatty acid. It is a benzene dicarboxylic acid used primarily in the production of various polymers and plastics.

Question 5

Which of these is synthetic polymer:

Accepted Answer

D. Polyester — Polyester is a synthetic polymer made through the reaction of dicarboxylic acids with diols. It is widely used in various applications, including textiles, packaging, and plastics. Polyesters can be produced through chemical processes in industry and are not naturally occurring polymers.

Question 6

Which is not a calcarious material:

Accepted Answer

B. Clay — Clay is not a calcareous material. It is a type of soil or sediment composed of fine-grained minerals and particles, primarily silicates. While clay may contain some calcium carbonate depending on its composition and origin, it is not predominantly composed of calcareous materials like lime, marble, or marine shells.

Question 7

Ecosystem is a smaller unit of:

Accepted Answer

C. Biosphere — Biosphere is the region of earth capable of supporting life. It includes lower atmosphere, the oceans, rivers, lakes, soils and solid sediments that actively interchange materials with all types of living organisms i.e., human beings, animals and plants. Ecosystem is a smaller unit of biosphere which consists of community of organisms and their interaction with environment i.e., animals, plants and microorganisms which lie in a definite zone

Question 8

In purification of potable water the coagullant used is:

Accepted Answer

D. Alum — Alum, specifically aluminum sulfate [Al2(SO4)3], is a commonly used coagulant in the purification of potable water. When added to water, alum forms aluminum hydroxide floc, which attracts suspended particles, colloids, and other impurities, causing them to clump together and settle out of the water. This process, known as coagulation, helps to clarify the water and remove impurities, making it suitable for drinking.

Question 9

The oxide of which element is basic:

Accepted Answer

A. Sodium — Sodium oxide (Na₂O) is a basic oxide. When it reacts with water, it forms sodium hydroxide (NaOH), which is a strong base. The presence of metal cations in the oxide contributes to its basic properties.

Question 10

Chile saltpetre has formula:

Accepted Answer

B. NaNO3 — Sodium nitrate, also known as chile saltpetre, has the chemical formula NaNO₃. It is a naturally occurring mineral found in Chile and is used in fertilizers, food preservation, and the production of explosives.

Question 11

Formula of orthoboric acid is:

Accepted Answer

A. H3BO3 — This is the correct formula of orthoboric acid, consisting of one boron atom, three hydrogen atoms, and three oxygen atoms.

Question 12

The catalyst used in contact process is:

Accepted Answer

D. V2O5 — Vanadium(V) oxide is the catalyst used in the contact process for the manufacture of sulfuric acid.

Question 13

Which is the strongest acid?

Accepted Answer

D. HClO4 — The acid strength increases with the increase in the number of oxygen atoms. As the oxidation state of the halogen increases, the bonding electrons are shifted away from the Hatom and the tendency of the molecule to lose a proton increases. This accounts for the change of strength of oxyacids. The oxyacids of halogens show their strength in the order given below:HXO4>HXO3 >HXO2 >HXO

Question 14

Coordination number of iron in [ Fe(CO)5] is:

Accepted Answer

D. 5 — In the complex [Fe(CO)5], iron is surrounded by five carbon monoxide ligands, resulting in a coordination number of 5.

Question 15

Trigonal shape is associated with:

Accepted Answer

D. dsp2 — The trigonal shape is associated with the dsp2 hybridization. In dsp2 hybridization, one s, three d, and two p orbitals hybridize to form five sp3 d-orbitals, which are arranged in a trigonal bipyramidal geometry.

Question 16

Synthetic rubber is made by the polymerization of:

Accepted Answer

D. Chloroprene — When acetylene is passed through an acidic solution of cuprous chloride and ammonium chloride and then allowed to stand for several hours at room temperature, vinyl acetylene and divinyl acetylene are obtained. If HCl is added to vinyl acetylene, chloroprene is obtained which readily polymerize to neoprene, used as synthetic rubber.

Question 17

Which reaction is not given by benzene?

Accepted Answer

B. Elimination — Benzene does not readily undergo elimination reactions. Elimination reactions typically involve the removal of atoms or groups from a molecule to form a double or triple bond. However, benzene's stability due to its aromaticity prevents it from participating in elimination reactions to form double or triple bonds. Instead, it favors substitution reactions.

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