JSMU Karachi Entry Test Chemistry S & P Block Elements — Set 2

S & P Block Elements MCQs set 2 for JSMU Karachi Entry Test Chemistry — 20 solved questions.

JSMU Karachi Entry Test Chemistry S & P Block Elements — Set 2

  1. Question 1

    Q1. A lab technician ignites a piece of sodium metal in a container with a limited supply of dry air. Which oxide is predominantly formed?

    • A) Sodium peroxide
    • B) Sodium monoxide
    • C) Sodium superoxide
    • D) Sodium ozonide

    Answer: Sodium monoxide

    Explanation: Sodium forms a stable monoxide in limited oxygen; sodium peroxide is the tempting distractor but requires excess oxygen for formation.

  2. Question 2

    Q2. A student observes that only one alkali metal reacts directly with nitrogen gas at room temperature to form a stable nitride. Identify this metal.

    • A) Lithium
    • B) Sodium
    • C) Potassium
    • D) Rubidium

    Answer: Lithium

    Explanation: Lithium is the only alkali metal reacting directly with nitrogen; Magnesium is tempting because it also forms nitrides but belongs to Group IIA.

  3. Question 3

    Q3. A sample of Magnesium nitrate is heated strongly in a test tube. Which set of products is released during this thermal decomposition mechanism?

    • A) Oxygen and Nitrogen gas
    • B) Magnesium nitrite and Oxygen
    • C) Magnesium oxide, Nitrogen dioxide, and Oxygen
    • D) Magnesium nitride and Oxygen

    Answer: Magnesium oxide, Nitrogen dioxide, and Oxygen

    Explanation: Group IIA nitrates decompose into metal oxides and NO2; lithium nitrate is tempting as it behaves similarly despite being a Group IA metal.

  4. Question 4

    Q4. During the laboratory preparation of Boric acid, Borax is treated with a concentrated mineral acid like HCl. What is the primary acidic product?

    • A) Boron trichloride
    • B) Sodium hydride
    • C) Metaboric acid
    • D) Orthoboric acid

    Answer: Orthoboric acid

    Explanation: Reaction of Borax with HCl yields Boric acid and NaCl; Boron trichloride is tempting but requires direct chlorination of Boron at high heat.

  5. Question 5

    Q5. When an aluminum container is used to transport concentrated Nitric acid, the metal does not dissolve. What mechanism explains this chemical passivity?

    • A) Formation of Aluminum nitrate
    • B) Formation of a protective oxide layer
    • C) Reduction of acid to Hydrogen gas
    • D) Rapid dissolution of the metal

    Answer: Formation of a protective oxide layer

    Explanation: Concentrated Nitric acid renders Aluminum passive by forming an oxide layer; dilute acid is tempting but actually reacts to release nitrogen oxides.

  6. Question 6

    Q6. A person trapped in a poorly ventilated room with a coal heater suffers from hypoxia because a specific gas binds irreversibly to hemoglobin.

    • A) Carbon monoxide
    • B) Carbon dioxide
    • C) Nitrogen dioxide
    • D) Sulfur dioxide

    Answer: Carbon monoxide

    Explanation: CO binds to hemoglobin more strongly than O2; CO2 is tempting but it binds to different sites and with much lower affinity.

  7. Question 7

    Q7. In the industrial Ostwald process for manufacturing Nitric acid, which catalyst is employed during the step-wise oxidation of Ammonia to Nitric oxide?

    • A) Iron with Molybdenum promoter
    • B) Vanadium pentoxide
    • C) Platinum-Rhodium gauge
    • D) Nickel catalyst

    Answer: Platinum-Rhodium gauge

    Explanation: The Ostwald process uses Platinum-Rhodium catalyst to oxidize ammonia; Iron is tempting because it is used in the Haber process instead.

  8. Question 8

    Q8. A chemist adds water to Phosphorus trichloride (PCl3). Which phosphorus-containing acid is formed through the resulting vigorous hydrolysis mechanism?

    • A) Phosphoric acid
    • B) Phosphine gas
    • C) Hypophosphorous acid
    • D) Phosphorous acid

    Answer: Phosphorous acid

    Explanation: Hydrolysis of PCl3 yields Phosphorous acid (H3PO3); PCl5 is tempting as its hydrolysis produces Phosphoric acid (H3PO4) instead.

  9. Question 9

    Q9. Chlorine gas is bubbled through a cold, dilute aqueous solution of Sodium hydroxide. What are the products of this disproportionation reaction?

    • A) Sodium chlorate and NaCl
    • B) Sodium hypochlorite and NaCl
    • C) Sodium perchlorate and NaCl
    • D) Chlorine dioxide and NaCl

    Answer: Sodium hypochlorite and NaCl

    Explanation: Cold NaOH yields hypochlorite; hot NaOH is the tempting distractor which produces chlorate (NaClO3) through a different disproportionation pathway.

  10. Question 10

    Q10. Concentrated Sulfuric acid is poured over a sample of cane sugar, resulting in a black charring mass. What chemical mechanism occurs?

    • A) Dehydration of sugar to carbon
    • B) Oxidation of sugar to CO2
    • C) Hydrolysis of sugar to glucose
    • D) Sulfonation of the sugar ring

    Answer: Dehydration of sugar to carbon

    Explanation: Sulfuric acid acts as a powerful dehydrating agent on sugar; oxidizing agent is tempting but dehydration is the dominant visible reaction.

  11. Question 11

    Q11. To synthesize Xenon hexafluoride (XeF6), Xenon and Fluorine must be reacted at 300 degrees Celsius under high pressure in which specific ratio?

    • A) 1:1 ratio
    • B) 1:5 ratio
    • C) 1:20 ratio
    • D) 2:1 ratio

    Answer: 1:20 ratio

    Explanation: XeF6 requires a 1:20 ratio of Xe to F2; 1:1 or 1:5 ratios are tempting but produce XeF2 or XeF4.

  12. Question 12

    Q12. During a qualitative analysis, a student adds dilute H2SO4 to various Group IIA nitrates. Which metal ion produces the most insoluble sulfate precipitate?

    • A) Magnesium sulfate
    • B) Calcium sulfate
    • C) Strontium sulfate
    • D) Barium sulfate

    Answer: Barium sulfate

    Explanation: Barium sulfate is highly insoluble due to high lattice energy; Magnesium sulfate is tempting but it is actually highly soluble.

  13. Question 13

    Q13. A sample of Orthoboric acid (H3BO3) is heated carefully in a crucible to exactly 100 degrees Celsius. What is the resulting product?

    • A) Boric anhydride
    • B) Tetraboric acid
    • C) Metaboric acid
    • D) Boron carbide

    Answer: Metaboric acid

    Explanation: Orthoboric acid first loses water at 100C to form Metaboric acid; Tetraboric acid is tempting but forms at higher temperatures (140C).

  14. Question 14

    Q14. In a metallurgical process, powdered silicon is reacted with a hot concentrated solution of sodium hydroxide. Identify the gas evolved in this mechanism.

    • A) Oxygen gas
    • B) Hydrogen gas
    • C) Methane gas
    • D) Silane gas

    Answer: Hydrogen gas

    Explanation: Silicon reacts with hot NaOH to produce Sodium silicate and Hydrogen; Oxygen is tempting but it is not a product of this displacement.

  15. Question 15

    Q15. Nitrogen dioxide (NO2) is dissolved in cold water as part of an acid rain simulation. Which two acids are produced by this disproportionation?

    • A) Nitric acid and Nitrous acid
    • B) Nitric acid and Nitric oxide
    • C) Nitrous acid and Nitrogen gas
    • D) Nitric acid only

    Answer: Nitric acid and Nitrous acid

    Explanation: NO2 reacts with water to give both HNO3 and HNO2; purely HNO3 is tempting but requires the presence of excess oxygen.

  16. Question 16

    Q16. In the Contact Process for the industrial production of Sulfuric acid, which catalyst facilitates the conversion of SO2 to SO3?

    • A) Finely divided Iron
    • B) Vanadium pentoxide
    • C) Manganese dioxide
    • D) Silver oxide

    Answer: Vanadium pentoxide

    Explanation: Vanadium pentoxide is the standard catalyst for SO2 oxidation; Platinum is tempting because it was used historically but is now outdated.

  17. Question 17

    Q17. Chlorine is widely used in the paper industry for bleaching wood pulp. What is the fundamental chemical mechanism of its bleaching action?

    • A) Reduction mechanism
    • B) Dehydration mechanism
    • C) Oxidation mechanism
    • D) Substitution mechanism

    Answer: Oxidation mechanism

    Explanation: Chlorine bleaches via the formation of nascent oxygen; SO2 is tempting as it bleaches via reduction, but the question specifies Chlorine.

  18. Question 18

    Q18. A miner uses a carbide lamp where water drips onto Calcium carbide (CaC2). Which flammable gas is generated to provide the flame?

    • A) Methane
    • B) Ethane
    • C) Ethene
    • D) Ethyne

    Answer: Ethyne

    Explanation: Calcium carbide reacts with water to produce Ethyne (Acetylene); Methane is tempting but comes from Aluminum carbide hydrolysis instead.

  19. Question 19

    Q19. A white precipitate of Silver chloride (AgCl) is treated with an excess of aqueous Ammonia. Why does the precipitate dissolve?

    • A) Diamminesilver(I) chloride
    • B) Silver nitride
    • C) Silver amide
    • D) Ammonium chloride

    Answer: Diamminesilver(I) chloride

    Explanation: AgCl dissolves in NH3 by forming a soluble diamminesilver(I) complex; silver nitride is tempting but is an explosive solid, not a solution.

  20. Question 20

    Q20. An artist wishes to etch a design onto a glass surface. Which halogen acid must be used due to its unique reactivity with silicates?

    • A) Hydrochloric acid
    • B) Hydrobromic acid
    • C) Hydrofluoric acid
    • D) Hydriodic acid

    Answer: Hydrofluoric acid

    Explanation: HF reacts with silicates in glass to form soluble Na2SiF6 or SiF4; HCl is tempting but cannot break the Si-O bonds.

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Level 1

A lab technician ignites a piece of sodium metal in a container with a limited supply of dry air. Which oxide is predominantly formed?