Punjab Chemistry 2019 — Solved MCQs

Question 1

For which mechanism, the first step involved is the same?

Accepted Answer

D. E1 and S,1 — E1: Leaving group departure followed by carbocation formation and deprotonation.S,1: Leaving group departure followed by nucleophilic attack.

Question 2

Ethanol can be converted into ethanoic acid by:

Accepted Answer

C. Oxidation — Ethanol can be oxidized to form ethanoic acid. This process typically involves the use of an oxidizing agent such as potassium dichromate (K2Cr2O7) or potassium permanganate (KMnO4) in the presence of an acidic medium.

Question 3

The carbon atom of a carbonyl group is:

Accepted Answer

B. sp2 hybridized — Organic compounds containing the carbonyl functional group, are called carbonyl compounds. In a carbonyl group, a carbon atom is bonded to oxygen with a double bond. It is sp2 hybridized.

Question 4

Which reagent is used to reduce carboxylic group to alcoholic group?

Accepted Answer

D. LiAlH4 — Lithium aluminum hydride is a powerful reducing agent commonly used to reduce carboxylic acids (and their derivatives) to alcohols.

Question 5

Which one of the following polymers is an addition polymer?

Accepted Answer

B. Polystyrene — Polystyrene is indeed an addition polymer. It's formed through the addition polymerization of styrene monomers, where the double bond in styrene opens up and links with other styrene molecules.

Question 6

Micronutrients are required in quantity ranging from:

Accepted Answer

C. 6-200 gm — This range is more reasonable, but still, it's on the higher side. Micronutrients are generally required in smaller quantities.

Question 7

Peroxyacetylnitrate (PAN) is an irritant to human beings and it affects:

Accepted Answer

D. Nose — PAN exposure can irritate the nasal passages, causing symptoms such as nasal congestion, runny nose, and irritation.

Question 8

Newspaper can be recycled again and again by how many times?

Accepted Answer

D. 5 — 5 is correct because newspaper can typically be recycled about 5 to 7 times before the fibers become too short and weak to be used again in high-quality paper products. After multiple recycling cycles, the fibers become too degraded to be effectively reprocessed into new paper, so they are often used for lower-grade paper products or other materials.

Question 9

Keeping in view the size of atoms, which order is the correct one:

Accepted Answer

B. Ba > Mg — Ba and magnsium are in same group . Ba comes after Mg it means it has more shell so it has large atomic sizeAtomic Radius:Atoms are so small that it is impossible to see an atom even with a powerful optical microscope. The size of a single atom therefore cannot be directly measured. However, techniques have been developed which can measure the distance between the centres of two bonded atoms of any element. Half of this distance is considered to be the radius of the atom. In the periodic table, the atomic radius increases from top to bottom within a group due to increase in atomic number . This is because of the addition of an extra shell of electrons in each period. In a period, however, as the atomic number increases from left to right, the atomic radius decreases . This gradual decrease in the radius is due to increase in the positive charge in the nucleus . As the positive nuclear charge increases, the negatively charged electrons in the shells are pulled closer to the nucleus. Thus, the size of the outermost shell becomes gradually smaller. This effect is quite remarkable in the elements of longer periods in which “d” and “f ” subshells are involved. For example, the gradual reduction in the size of Lanthanides is significant and called Lanthanide Contraction.

Question 10

Tincal is a mineral of:

Accepted Answer

B. B — Borax is the sodium salt of tetraboric acid. It is the most important of all borates .Borax occurs as a natural deposit called tincal in the dried up lakes of Tibet and California.Borax may also be obtained from tincal (Na2B4O7.10H2O) by treating tincalwith water and subsequently evaporating the clear solution, when crystalsof borax separate out.

Question 11

Laughing gas is chemically:

Accepted Answer

B. N2O — Nitrous oxide, commonly known as laughing gas or happy gas, is a colorless, non-flammable gas. This gas is used in medical and dental procedures as a sedative. It helps to relieve anxiety before the procedure and allow the patient to relax

Question 12

Which one of the following hydrogen halides is the weakest acid in aqueous solution?

Accepted Answer

A. HF — Hydrofluoric acid (HF) is the weakest acid among the hydrogen halides. This is because fluorine is the most electronegative element among the halogens, resulting in a strong hydrogen-fluorine bond that is less likely to dissociate in aqueous solution, making HF a weaker acid.

Question 13

Which one of the following sulphate is insoluble in water?

Accepted Answer

D. Barium sulphate — Barium sulphate is insoluble in water. It forms a white precipitate when mixed with water due to its low solubility. Unlike the other options, barium sulphate does not dissociate into ions when mixed with water, leading to its insolubility.

Question 14

Which one of the following is a typical transition metal?

Accepted Answer

C. Co — Cobalt is a well-known transition metal with a variety of applications. It's used in the production of magnetic materials, rechargeable batteries, and as a catalyst in chemical reactions.

Question 15

Which set of hybrid orbital has planar triangular shape?

Accepted Answer

B. sp2 — This hybridization involves one s orbital and two p orbitals, resulting in three hybrid orbitals. These orbitals are arranged in a trigonal planar geometry, forming a planar triangular shape.

Question 16

Formula of chloroform is:

Accepted Answer

D. CHCl3 — CH3Cl is chloromethane.CH2Cl2 is dichloromethane.CHCl3 is trichloromethane (chloroform).CCL4 is tetrachloromethane (Carbon Tetrachloride).

Question 17

During nitration of benzene, the active nitrating agent is:

Accepted Answer

B. NO+2 — Nitration of benzene: Nitric acid and sulfuric acid used in nitration generate nitronium NO2+ ions as electrophiles. Nitronium NO2+ is the nitrating agent.

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