NUST NET Medical / Biological Sciences Chemistry: S & P Block Elements MCQs

NUST NET Medical / Biological Sciences Chemistry: S & P Block Elements MCQs — sample questions

1. Question 1

   Q1. A student compares the solubility of Group 2 sulfates and finds that Magnesium sulfate is soluble while Barium sulfate is insoluble. This trend occurs because:

   • A) Lattice energy of Magnesium sulfate is higher than Barium sulfate
   • B) Hydration energy of Magnesium ion is much higher than Barium ion
   • C) Electronegativity of Barium is higher than Magnesium
   • D) Ionic radius of Magnesium is larger than Barium

   Answer: Hydration energy of Magnesium ion is much higher than Barium ion

   Explanation: Magnesium sulfate has a high hydration energy that outweighs its lattice energy, unlike Barium sulfate which has a dominant lattice energy.

2. Question 2

   Q2. When heating Group 1 carbonates, Lithium carbonate decomposes into its oxide, but Sodium carbonate remains stable. This difference is due to:

   • A) Lithium ion has a higher charge density than Sodium ion
   • B) Sodium carbonate is more covalent than Lithium carbonate
   • C) Lithium ion is larger than the Sodium ion
   • D) Sodium carbonate decomposes at a lower temperature than Lithium carbonate

   Answer: Lithium ion has a higher charge density than Sodium ion

   Explanation: Lithium has a high charge density which polarizes the carbonate ion, leading to decomposition; Sodium has a lower charge density.

3. Question 3

   Q3. In Group 14, Tin commonly forms stable +4 compounds, whereas Lead is more stable in the +2 oxidation state. What causes this contrast?

   • A) Lead is more electronegative than Tin
   • B) Tin has a larger atomic radius than Lead
   • C) The inert pair effect is more pronounced in Lead than in Tin
   • D) Tin +2 compounds are more powerful oxidizing agents than Lead +2

   Answer: The inert pair effect is more pronounced in Lead than in Tin

   Explanation: Lead exhibits the inert pair effect more strongly than Tin, making the +2 state more stable for Lead.

4. Question 4

   Q4. Burning Lithium in excess oxygen yields Lithium oxide (Li2O). In contrast, burning Sodium in excess oxygen primarily produces which compound?

   • A) Na2O
   • B) NaO2
   • C) NaO
   • D) Na2O2

   Answer: Na2O2

   Explanation: Sodium forms a peroxide (Na2O2) with excess oxygen, whereas Lithium only forms a normal oxide (Li2O) due to size constraints.

5. Question 5

   Q5. When manufacturing bleaching powder, the Hasenclever and Bachmann processes differ significantly in their mechanical design. Which statement correctly identifies the Hasenclever apparatus?

   • A) Bachmann process uses horizontal cylinders
   • B) Hasenclever process uses horizontal cylinders with rotating shafts
   • C) Hasenclever process is a vertical tower method
   • D) Bachmann process is only used for liquid chlorine

   Answer: Hasenclever process uses horizontal cylinders with rotating shafts

   Explanation: The Hasenclever process utilizes a series of cylinders with rotating shafts, whereas the Bachmann process uses a vertical tower design.

6. Question 6

   Q6. A chemist performs a Borax bead test in an oxidizing flame. If the metal ion present is Copper, what color is the bead?

   • A) Blue
   • B) Green
   • C) Yellow
   • D) Red

   Answer: Blue

   Explanation: Copper produces a blue bead in an oxidizing flame, whereas Chromium produces a green bead in the same conditions.

7. Question 7

   Q7. Comparing the allotropes of Phosphorus, White phosphorus is much more reactive and poisonous than Red phosphorus because White phosphorus:

   • A) White phosphorus is a polymer and less reactive
   • B) Red phosphorus consists of discrete P4 molecules
   • C) White phosphorus consists of discrete P4 tetrahedral molecules
   • D) Red phosphorus is soluble in Carbon disulfide

   Answer: White phosphorus consists of discrete P4 tetrahedral molecules

   Explanation: White phosphorus consists of discrete P4 molecules and is highly reactive, whereas Red phosphorus is a stable macromolecular polymer.

8. Question 8

   Q8. Lithium shows a diagonal relationship with Magnesium. Which chemical property is shared by both Lithium and Magnesium but not by Sodium?

   • A) Reaction with Carbon dioxide
   • B) Formation of acidic oxides
   • C) High solubility of their carbonates
   • D) Direct formation of nitrides upon heating in air

   Answer: Direct formation of nitrides upon heating in air

   Explanation: Lithium and Magnesium both react directly with Nitrogen to form nitrides, a similarity not shared by other Group 1 elements.

9. Question 9

   Q9. Graphite conducts electricity while Diamond acts as an insulator. This contrast in electrical conductivity is primarily due to the fact that:

   • A) Diamond is sp2 hybridized
   • B) Graphite is sp2 hybridized with delocalized electrons
   • C) Graphite is sp3 hybridized
   • D) Diamond has delocalized pi electrons

   Answer: Graphite is sp2 hybridized with delocalized electrons

   Explanation: Graphite uses sp2 hybridization leaving one free electron for conduction, while Diamond uses sp3 with all electrons localized in bonds.

10. Question 10

    Q10. The boiling point of Ammonia (-33.4 C) is significantly higher than that of Phosphine (-87.7 C). This contrast is explained by:

    • A) Nitrogen is more electronegative than Phosphorus, allowing hydrogen bonding
    • B) Phosphine has a higher molecular mass than Ammonia
    • C) Ammonia has a lower dipole moment than Phosphine
    • D) Phosphorus atoms are smaller than Nitrogen atoms

    Answer: Nitrogen is more electronegative than Phosphorus, allowing hydrogen bonding

    Explanation: Ammonia has a higher boiling point than Phosphine because Nitrogen is highly electronegative, allowing for strong intermolecular hydrogen bonding.

11. Question 11

    Q11. Beryllium oxide (BeO) and Magnesium oxide (MgO) differ in their chemical nature. Which statement correctly differentiates their reactivity?

    • A) BeO is purely acidic
    • B) MgO is amphoteric
    • C) BeO is amphoteric while MgO is basic
    • D) Both BeO and MgO are neutral oxides

    Answer: BeO is amphoteric while MgO is basic

    Explanation: Beryllium oxide is amphoteric and reacts with both acids and bases, whereas Magnesium oxide is purely basic.

12. Question 12

    Q12. When comparing the physical properties of Noble gases, which element possesses the lowest boiling point and is hardest to liquefy?

    • A) Neon
    • B) Helium
    • C) Argon
    • D) Krypton

    Answer: Helium

    Explanation: Helium has the lowest boiling point of all known substances due to extremely weak London dispersion forces.

13. Question 13

    Q13. Comparing the oxyacids of Chlorine, Perchloric acid (HClO4) is a much stronger acid than Chloric acid (HClO3) because:

    • A) HClO3 has more oxygen atoms than HClO4
    • B) Chlorine has a lower oxidation state in HClO4
    • C) HClO3 is a stronger oxidizing agent than HClO4
    • D) HClO4 has a higher number of oxygen atoms which stabilizes the anion

    Answer: HClO4 has a higher number of oxygen atoms which stabilizes the anion

    Explanation: Perchloric acid is stronger because the higher number of oxygen atoms increases the oxidation state and polarizes the O-H bond.

14. Question 14

    Q14. Boron and Aluminum are both in Group 13, but their halides behave differently. Which statement correctly contrasts BCl3 and AlCl3?

    • A) BCl3 forms a stable dimer
    • B) AlCl3 is always monomeric in the vapor phase
    • C) AlCl3 exists as a dimer (Al2Cl6) in the vapor phase
    • D) BCl3 has a higher boiling point than AlCl3

    Answer: AlCl3 exists as a dimer (Al2Cl6) in the vapor phase

    Explanation: Aluminum chloride forms a dimer (Al2Cl6) to complete its octet, whereas Boron trichloride remains a monomeric trigonal planar molecule.

15. Question 15

    Q15. In the Solvay process, the separation of Sodium bicarbonate from the reaction mixture depends on its solubility contrast with Sodium carbonate. Which is true?

    • A) NaHCO3 is less soluble in water than Na2CO3
    • B) Na2CO3 is less soluble in water than NaHCO3
    • C) Both have equal solubility in water
    • D) NaHCO3 is only soluble in hot alcohol

    Answer: NaHCO3 is less soluble in water than Na2CO3

    Explanation: Sodium bicarbonate is less soluble than Sodium carbonate, which allows it to precipitate in the Solvay process tower.

16. Question 16

    Q16. Carbon dioxide (CO2) is a gas at room temperature, while Silicon dioxide (SiO2) is a high-melting solid. This contrast is due to:

    • A) CO2 is a solid macromolecule at room temperature
    • B) SiO2 forms a giant covalent crystal lattice
    • C) SiO2 consists of discrete linear molecules
    • D) CO2 has a higher melting point than SiO2

    Answer: SiO2 forms a giant covalent crystal lattice

    Explanation: CO2 is a discrete gas molecule with weak forces, whereas SiO2 is a giant covalent macromolecule with high melting points.

17. Question 17

    Q17. Halogens act as oxidizing agents. When comparing their power to displace other halogens from halides, which is the most powerful?

    • A) Iodine
    • B) Bromine
    • C) Fluorine
    • D) Chlorine

    Answer: Fluorine

    Explanation: Fluorine is the strongest oxidizing agent among halogens and can displace all other halide ions from their solutions.

18. Question 18

    Q18. A scientist heats Lithium nitrate and Potassium nitrate in separate crucibles. What is the key difference in the products formed?

    • A) Lithium nitrate produces Nitrogen dioxide gas
    • B) Potassium nitrate produces Nitrogen dioxide gas
    • C) Both produce the metal oxide and NO2
    • D) Both produce the metal nitrite and O2

    Answer: Lithium nitrate produces Nitrogen dioxide gas

    Explanation: Lithium nitrate decomposes to Li2O, NO2, and O2, while Potassium nitrate only decomposes to KNO2 and O2.

19. Question 19

    Q19. Orthoboric acid (H3BO3) appears to have three hydrogen atoms, yet its acidity contrasts with typical triprotic acids because:

    • A) It is a strong tribasic acid
    • B) It donates three protons in aqueous solution
    • C) It is a strong Brönsted acid
    • D) It is a weak monobasic Lewis acid

    Answer: It is a weak monobasic Lewis acid

    Explanation: Orthoboric acid is a weak monobasic acid that acts as a Lewis acid by accepting an OH- ion from water.

20. Question 20

    Q20. Rhombic sulfur and Monoclinic sulfur are two allotropic forms. At what specific transition temperature do these two forms coexist in equilibrium?

    • A) 113 C
    • B) 95.5 C
    • C) 119 C
    • D) 444 C

    Answer: 95.5 C

    Explanation: 95.5 C is the transition temperature where rhombic and monoclinic sulfur coexist in equilibrium at one atmospheric pressure.