Free s-Block and p-Block Elements MCQs with Answers

• A. Almost pure water
• B. Almost pure hydrogen peroxide
• C. A mixture of water and hydrogen peroxide
• D. None of these

Explanation: Atomic hydrogen reacts with O₂ stepwise (H· → HO₂· → H₂O₂), and this pathway strongly favors hydrogen peroxide formation.

• A. Saturation of water with MgCO3
• B. Saturation of water with CaSO4
• C. Addition of Na2SO4 to water
• D. Saturation of water with CaCO3

Explanation: Hardness in water is caused by the presence of dissolved calcium (Ca²⁺) and magnesium (Mg²⁺) ions.

• A. CO and H2 are fractionally separated using Copper Chloride solution
• B. CO is removed by absorption in aqueous Cu2Cl2 solution
• C. H2 is removed through occlusion with Pd
• D. CO is oxidized to CO2 with steam in the presence of a catalyst followed by absorption of CO2 in an alkaline solution

Explanation: This describes the water-gas shift reaction. The initial mixture is treated with steam over a catalyst to convert the toxic CO into CO₂…

• A. Its tendency to lose an electron to form a cation
• B. Its tendency to gain a single electron in its valence shell to attain stable electronic configuration
• C. Its electron-gain enthalpy value is low, i.e. only slightly negative
• D. Its small size

Explanation: The most significant similarity between hydrogen and the halogens is their electronic structure.

• A. The ionization enthalpy of hydrogen resembles that of the alkali metals
• B. Its reactivity is similar to halogens
• C. It resembles both alkali metals and halogens
• D. Loss of an electron from a hydrogen atom results in a nucleus of a very small size

Explanation: A hydrogen ion (H⁺) is a bare proton with no electrons. This gives it an incredibly small size and a very high positive charge density.

• A. B2H6
• B. NH3
• C. H2O
• D. Both B and C

Explanation: Electron-rich hydrides are those where the central atom has one or more lone pairs of electrons after forming bonds with hydrogen.

• A. LiH > NaH > CsH > KH > RbH
• B. LiH < NaH < KH < RbH < CsH
• C. RbH > CsH > NaH > KH > LiH
• D. NaH > CsH > RbH > LiH > KH

Explanation: The ionic character of a bond is determined by the difference in electronegativity between the two atoms.

• A. Fluorine
• B. Nitrogen
• C. Carbon
• D. Hydrogen

Explanation: Atomic size generally decreases across a period from left to right due to increasing nuclear charge.

• A. An oxidizing agent in both (A) and (B)
• B. An oxidizing agent in (A) and a reducing agent in (B)
• C. A reducing agent in (A) and an oxidizing agent in (B)
• D. A reducing agent in both (A) and (B)

Explanation: In reaction (A), H₂O₂ is reduced while oxidizing I⁻ to I₂, so it acts as an oxidizing agent.

• A. Liquid hydrogen + liquid oxygen
• B. Liquid oxygen + liquid nitrogen
• C. Both a and b
• D. None of these

Explanation: A rocket propellant requires a fuel and an oxidizer that react to produce a large amount of hot gas for thrust.

• A. Reaction of methane with steam
• B. Mixing natural hydrocarbons of high molecular weight
• C. Electrolysis of water
• D. Reaction of ionic hydrides with water

Explanation: The electrolysis of pure water (often containing a small amount of an electrolyte like NaOH or H₂SO₄ to conduct current) produces…

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

Explanation: Argon is chemically inert and does not react with metals at high temperatures.

• A. Hydrogen sulfide
• B. Water
• C. HCl
• D. None of these

Explanation: Hydrogen (H₂) reacts with oxygen during combustion to form H₂O. The reaction is highly exothermic, releasing a lot of energy.

• A. H2O
• B. H2S
• C. H2Se
• D. H2Te

Explanation: Boiling points depend on intermolecular forces. H₂O has strong hydrogen bonding, giving it the highest boiling point.

• A. Ca
• B. Cu
• C. Zn
• D. Fe

Explanation: Hydrogen reacts directly with highly reactive metals, such as the alkali and most alkaline earth metals, to form ionic (saline) hydrides.

• A. Si
• B. Ba
• C. Mg
• D. Ca

Explanation: Magnesium (Mg) is the central atom in the chlorophyll molecule. It plays a key role in absorbing light energy during photosynthesis.

• A. Thenard, Urey
• B. Urey, Rutherford
• C. Urey, Thenard
• D. Aston, Chadwick

Explanation: Hydrogen peroxide (H₂O₂) was first isolated and described by Louis Jacques Thénard in 1818.

• A. D₂O
• B. H₂O
• C. O₃
• D. Dil. HCl

Explanation: Ozone (O₃) is a powerful oxidizing agent. It can oxidize liquid mercury (Hg), causing it to lose its meniscus and stick to glass, a…

• A. NaNO3
• B. Pb (NO3)2
• C. ZnO
• D. H2O2

Explanation: Hydrogen peroxide (H₂O₂) decomposes upon heating to release O₂. It acts as an oxidizing agent with KI to produce I₂ (brown colour) and as…

• A. A blue colour is obtained in ether due to formation of Cr2(SO4)3
• B. A blue colour is obtained in ether due to formation of CrO5
• C. A blue colour is obtained in ether due to formation of CrO3
• D. Chromyl chloride is formed

Explanation: This is a characteristic test for chromates. In the presence of acid and H₂O₂, the dichromate ion is converted into chromium(VI) peroxide…