Sindh Mdcat Exclusive Course Chemistry S And P Block Elements — Solved MCQs

Question 1

HCl is added to the following oxides. Which one would give H₂O₂?

Accepted Answer

C. BaO2 — Hydrogen peroxide (H₂O₂) is formed by the reaction of an acid with a peroxide. Barium peroxide (BaO₂) reacts with HCl to form BaCl₂ and H₂O₂. The other oxides listed are not peroxides.

Question 2

When the same amount of zinc is treated separately with excess of sulphuric acid and excess of sodium hydroxide, the ratio of volumes of hydrogen evolved is:

Accepted Answer

A. 1 : 1 — The balanced chemical equations are Zn + H₂SO₄ → ZnSO₄ + H₂ and Zn + 2NaOH → Na₂ZnO₂ + H₂. In both cases, one mole of zinc produces one mole of hydrogen gas. Therefore, the ratio of the volumes of H₂ evolved is 1:1.

Question 3

Which is the strongest base?

Accepted Answer

A. NaOH — Sodium hydroxide (NaOH) is the strongest base among the options because it is the hydroxide of a Group 1 alkali metal. It is a strong electrolyte that dissociates completely in water to produce a high concentration of OH⁻ ions.

Question 4

An example of a covalent hydride is:

Accepted Answer

D. AsH3 — Covalent hydrides are formed when hydrogen bonds with nonmetals or metalloids. Arsine (AsH₃) is a covalent hydride because arsenic (As) is a metalloid. The other options are ionic (saline) hydrides formed with alkali or alkaline earth metals.

Question 5

H2O2 cannot be synthesized by:

Accepted Answer

B. Addition of ice cold H2SO4 on PbO2 — Lead dioxide (PbO₂) is not a peroxide but a true oxide of lead in the +4 oxidation state. It reacts with sulfuric acid in an acid-base reaction, not a redox reaction that would produce hydrogen peroxide. The other methods listed are valid synthesis routes for H₂O₂.

Question 6

Which one of the following processes will produce hard water?

Accepted Answer

B. Saturation of water with CaSO4 — Hardness in water is caused by the presence of dissolved calcium (Ca²⁺) and magnesium (Mg²⁺) ions. Calcium sulfate (CaSO₄) is a salt that dissolves in water to produce Ca²⁺ ions, thus contributing to permanent hardness.

Question 7

Which one of the following statements is incorrect with regard to ortho and para isomers of hydrogen?

Accepted Answer

B. The ortho isomer has zero nuclear spin whereas the para isomer has one nuclear spin — The correct answer is Option B. The statement that 'The ortho isomer has zero nuclear spin whereas the para isomer has one nuclear spin' is incorrect. In reality, the ortho hydrogen has parallel spins, resulting in a higher total nuclear spin of 1, while para hydrogen has antiparallel spins, resulting in a total nuclear spin of 0. Thus, the ortho isomer has a higher energy state compared to the para isomer. Option A is true because ortho and para hydrogen are indeed nuclear spin isomers. Option C is also true because the para isomer, being lower in energy, is more stable and favored at lower temperatures. Option D incorrectly states the thermal conductivity relationship; actually, ortho hydrogen has higher thermal conductivity due to more available rotational states.

Question 8

4D2O + 3Fe → Fe3O4 + gas. The gas produced in the above reaction is:-

Accepted Answer

C. D2 — The reaction is the reaction between heavy water (deuterium oxide, 4D2O) and iron (Fe) to produce a compound called iron(III) oxide (Fe3O4) and gas. The gas produced in this reaction is deuterium gas (2D2), which is a form of hydrogen gas composed of deuterium atoms (D) instead of normal hydrogen atoms (H). Deuterium is a heavy isotope of hydrogen and is used in various scientific and industrial applications, including nuclear reactors and nuclear magnetic resonance (NMR) spectroscopy.

Question 9

Which of the following compound affects mercury:

Accepted Answer

C. O3 — The correct answer is O3 (ozone). Ozone oxidizes mercury, forming less volatile compounds that assist in its removal from the atmosphere, reducing pollution. Other options like heavy water, regular water, and dilute hydrochloric acid do not have the same impact on mercury's atmospheric cycling as ozone does.

Question 10

Which of the following is only acidic in nature?

Accepted Answer

C. B(OH)3 — Boric acid, B(OH)₃, is a weak Lewis acid, accepting an OH⁻ ion from water rather than donating a proton. Beryllium and aluminium hydroxides are amphoteric, while magnesium hydroxide is basic.

Question 11

Sodium carbonate reacts with SO2 in aqueous solution to give:

Accepted Answer

C. Na2SO3 — The correct answer is Option C: Na2SO3. Sodium carbonate reacts with SO2 in aqueous solution to give Na2SO3. The reaction can be represented as follows: Na2CO3 + SO2 → Na2SO3 + CO2Option A, B, and D are incorrect as they do not represent the correct product formed in the given chemical reaction.

Question 12

Sodium thiosulfate, Na₂S₂O₃ ·5H₂O, is used in photography to:

Accepted Answer

C. Remove undecomposed AgBr as soluble silver thiosulphate complex — In the photographic fixing process, sodium thiosulfate (hypo) is used to remove the unexposed and undeveloped silver bromide (AgBr) from the film. It does this by forming a stable, soluble complex ion, [Ag(S₂O₃)₂]³⁻, which can then be washed away.

Question 13

Na2CO3 can be manufactured by Solvay process but K2CO3 cannot be prepared because:

Accepted Answer

C. KHCO3 is more soluble than NaHCO3 — The Solvay process relies on the precipitation of bicarbonates. In the case of sodium, NaHCO3 is less soluble and precipitates out easily, allowing for the subsequent steps to produce Na2CO3. However, KHCO3 is more soluble and does not precipitate, making it unsuitable for the Solvay process to manufacture K2CO3. Thus, the correct answer is that KHCO3 is more soluble than NaHCO3. The other options incorrectly focus on the solubility of the carbonates themselves rather than the critical bicarbonate stage in the process.

Question 14

The bleaching action of bleaching powder is due to the formation of:

Accepted Answer

C. HClO — The correct answer is HClO. The bleaching action of bleaching powder is due to the formation of hypochlorous acid (HClO). In the presence of dilute acids, bleaching powder loses oxygen, which is used for oxidation and bleaching. The other options (CaCl2, CaSO4, Ca(ClO3)2) are incorrect as they do not play a role in the bleaching action of bleaching powder.

Question 15

Alkaline earth metals produce bright blue colour when they are dissolved in liquid ammonia. It is due to:

Accepted Answer

D. absorption of light by the solvated electrons. — Alkaline earth metals produce a bright blue color when dissolved in liquid ammonia due to the presence of solvated electrons. These solvated electrons absorb light in the visible region of the spectrum and emit light in the blue region, resulting in the blue color observed. The correct answer is the absorption of light by the solvated electrons. The other options are incorrect because they do not accurately describe the phenomenon responsible for the bright blue color.

Question 16

Which of the following statement is incorrect when a mixture of NaCl and K2Cr2O7 is strongly heated with conc. H2SO4?

Accepted Answer

C. Chlorine gas is evolved — When a mixture of NaCl and K2Cr2O7 is heated with conc. H2SO4, chlorine gas (Cl2) is evolved along with chromium trioxide (CrO3). The incorrect options provide misleading information about the products formed, such as colored vapors or formation of chromyl chloride. These are not the actual products formed in this reaction.

Question 17

The paramagnetic species is:

Accepted Answer

A. KO2 — KO2 (potassium superoxide) is the correct answer as it contains an unpaired electron, making it paramagnetic and attracted to a magnetic field. The other options (SiO2, TiO2, BaO2) are diamagnetic and do not exhibit paramagnetic properties due to the absence of unpaired electrons in their molecular structures.

Question 18

CsBr3 contains:

Accepted Answer

C. Cs+ and Br3– ions — CsBr3 is an ionic compound. Cs is a monovalent ion, i.e., Cs+. So, the other ion will be Br3−. Therefore, the correct answer is Cs+ and Br3− ions. Option A is incorrect as it implies covalent bonds in an ionic compound. Option B is incorrect as Cs does not have a 3+ charge. Option D is incorrect as Cs does not have a 3+ charge and Br does not have a 3− charge.

Question 19

Choose the incorrect statement.

Accepted Answer

B. BeF2 forms a complex compound with excess NaF, in which the complex entity containing Be, is a cation. — Option B is correct.Beryllium fluoride (BeF2) forms a complex compound with excess sodium fluoride (NaF), in which the complex entity containing Be is an anion. The complex is called sodium tetrafluoroberyllate (Na2[BeF4]2-). The formation of the complex can be represented by the following equation:BeF2 + 2NaF → Na2[BeF4]2- In the complex, the beryllium ion (Be2+) is surrounded by four fluoride ions (F-). The beryllium ion has a charge of +2, while each fluoride ion has a charge of -1. The overall charge of the complex is -2. The complex is an anion because it has a negative charge. The negative charge is due to the presence of the four fluoride ions. The fluoride ions are attracted to the beryllium ion because of the opposite charges.

Question 20

Cryolite is :

Accepted Answer

D. Sodium hexafluoroaluminate(III) — The correct answer is Option D: Sodium hexafluoroaluminate(III). Cryolite is an ore of sodium with the chemical formula Na3[AlF6], making the IUPAC name of this complex salt sodium hexafluoroaluminate(III). The other options, such as calcium fluoride and potassium hexafluoroaluminate, do not match the chemical composition and properties of cryolite.

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