Punjab Chemistry 2023 Paper 1 — Solved MCQs

Question 1

Pick the element having least melting point among alkaline earth metals?

Accepted Answer

A. Be — The melting and boiling points of IA and IIA group elements decrease from top to bottom due to the increase in their atomic sizes. The binding forces present between large sized atoms are relatively weaker as compared to those between smaller atoms.Across the short periods, the melting and boiling points of elements increase with the number of valence electrons upto group IVA and then decrease upto the noble gases. The melting points of group IA elements are low because each atom in them provides only one electron to form a bond with other atom. Melting points of group IIA elements are considerably higher than those of group IA elements because each atom in them provides two binding electrons.

Question 2

The mineral sylvite has the chemical formula:

Accepted Answer

B. KCl — The formula for sylvite is KCl.

Question 3

Boric acid cannot be used:

Accepted Answer

C. In soda bottles — Uses of Boric Acid1. Boric acid is used in medicines as an antiseptic, e.g. dusting powder, boricointment and boric solution is used as an eye-wash.2. It is used in pottery as a glaze because borate glazes are more fusible thansilicate glazes and possess a higher coefficient of expansion.3. It is also used in candle industry for stiffening of wicks.

Question 4

Oxidation of NO in air produces:

Accepted Answer

B. N2O4 — NO is oxidised by ozone in the atmosphere, on a time scale of tens of minutes, to give NO2. In rural air, away from sources of NO, most of the nitrogen oxides in the atmosphere are in the form of NO2.

Question 5

Which halogen docs occur naturally in positive oxidation state?

Accepted Answer

A. I2 — Among the halogens (fluorine, chlorine, bromine, iodine, and astatine), the only halogen known to naturally occur in a positive oxidation state is iodine.Iodine can occur in several oxidation states, including -1, 0, +1, +3, +5, and +7. However, the most common oxidation state of iodine in nature is -1 in compounds such as iodide salts (e.g., sodium iodide, potassium iodide).Nevertheless, iodine can also occur in the +1 oxidation state in certain compounds, such as iodine monoxide (IO). While iodine in the +1 oxidation state isn't as common as its -1 oxidation state, it does exist in some chemical compounds.

Question 6

The purest form of commetcial iron is:

Accepted Answer

C. Wrought iron — 1. Pig iron or cast iron 2.5 to 4.5% carbon 2. Wrought iron 0.12 to 0.25% carbon 3. Steel 0.25 to 2.5% carbon Wrought iron is the purest form of commercial iron and contains the lowest percentage of carbon and upto 0.3% of impurities like S,P,Si and Mn, etc.

Question 7

Which one of the following is not heterocyclic compound?

Accepted Answer

A. Naphthalene — The compounds in which the ring consists of atoms of more than one kind are called heterocyclic compounds or heterocycles. In heterocyclic compounds generally one or more atoms of elements such as nitrogen (N), oxygen (O) or sulphur (S) are present. The atom other than carbon viz, N, 0, or S, present in the ring is called a hetero atom. Naphthalene is an aromatic compound.

Question 8

The reaction step shown is known as:H3C-CH2 -OSO3H + H2O→1000C H3C—CH2 -OH+ H2SO2

Accepted Answer

B. Hydration — When alkenes are treated with cold concentrated sulphuric acid, they are dissolved because they react by addition to form alkyl hydrogen sulphate. These alkylhydrogen sulphates on boiling with water decompose to give corresponding alcohols. The overall reaction involves the addition of water to an alkene and it is, therefore, called hydration reaction.

Question 9

Predict the product in the reaction:

Accepted Answer

A. A — By distilling phenol with zinc dust, the product obtained is benzene.

Question 10

For which mechanism the first step involved is the same?

Accepted Answer

D. E1 and SN1 — In E1 mechanism, like SN1 mechanism, the first step is the slow ionization of the substrate to give a carbocation. In the second step, the nucleophile attacks on hydrogen to give an alkene as a product.

Question 11

Which compound shows maximum hydrogen bonding with water?

Accepted Answer

C. C2H5OH — Lower alcohols are generally colourless toxic liquids with characteristic sweet smell and burning taste They are readily soluble in water but solubility decreases in higher alcohols. The solubility of alcohols is due to hydrogen bonding which is prominent in lower alcohols but diminishes in higher alcohols.

Question 12

Which among the following is known as Carbolic acid?

Accepted Answer

A. C6H5 OH — Aromatic compounds which contain one or more OH groups directly attached with carbon of benzene ring are called Phenols. The simplest example is phenol which is also known as Carbolic acid

Question 13

Ketones are prepared by oxidation of:

Accepted Answer

B. Secondary alcohol — Oxidation of alcohols convert them into aldehydes and ketones. The best reagent for this purpose is acid dichromate. Primary alcohols yield aldehydes whereas secondary alcohols yield ketones. Tertiary alcohols are resistant to oxidation.

Question 14

Acctamide is prepared by heating:

Accepted Answer

A. Ammonium acetate — Carboxylic acids react with ammonia to form ammonium salts which on heating produce acid amides.

Question 15

Natural starch consists of how much percentage of amylose?

Accepted Answer

C. 10-20% — Starch is not a pure compound. It is a mixture of two polysaccharides, amylose and amylopectin which can be separated from one another. Amylose is soluble in water and gives a deep blue colour with iodine while amylopectin is insoluble and gives no colour. Natural starch consists of 10 to 20% amylose and 80 to 90% amylopectin.

Question 16

Micronutrients are required in the quantity ranging from:

Accepted Answer

B. 6-200g — Only minute amounts of these elements are needed for healthy plant growth and it may be dangerous to add too much quantity because they are poisonous in larger quantities. These are generally required in quantities ranging from 6 grams to 200 grams per acre.

Question 17

A single chloride free radical can destroy how many ozone molecules?

Accepted Answer

D. 105 — A single chloride free radical can destroy upto 100,000 ozone molecules.

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