P - Block MCQ Quiz - Objective Question with Answer for P - Block - Download Free PDF

CONCEPT:

Trends in Group-17 Elements (Halogens)

• The halogens include Fluorine (F), Chlorine (Cl), Bromine (Br), and Iodine (I).
• Covalent Radius: Increases down the group due to the addition of new shells (F < Cl < Br < I).
• Ionic Radius: Also increases as you go down the group (F⁻ < Cl⁻ < Br⁻ < I⁻).
• First Ionization Energy: Decreases down the group due to increasing atomic size (F > Cl > Br > I).
• Electron Affinity: Typically increases down the group, but fluorine shows an irregularity—it has lower electron affinity than chlorine despite being smaller.

EXPLANATION:

The order of first four elements of group-17 are as follows.
F < Cl < Br < I (Covalent radius)
Cl > F > Br > I (Electron affinity)
F– < Cl–< Br– < I– (Ionic radius)
F > Cl > Br > I (Ist ionization energy)
Electron affinity order is irregular. 

• Electron Affinity: The irregularity arises because fluorine is very small, and adding an extra electron leads to high electron–electron repulsion, reducing the energy released.
• All other properties—covalent radius, ionic radius, and first ionization energy—follow regular trends down the group without deviation in the first four elements.

Therefore, the correct answer is A, C and D only

CONCEPT:

Hydrolysis of Non-metal Halides

• Many non-metal halides like PCl₅, NCl₃, and SOCl₂ undergo hydrolysis with water to form corresponding oxoacids and ammonia.
• The nature of the product depends on the oxidation state and structure of the compound.

EXPLANATION:

• PCl₅ + 4H₂O → H₃PO₄ + 5HCl
  • Phosphorus pentachloride forms phosphoric acid (H₃PO₄) upon hydrolysis.
• NCl₃ + 3H₂O → NH₃ + 3HOCl
  • Nitrogen trichloride gives ammonia (NH₃) and hypochlorous acid.
• SOCl₂ + 2H₂O → H₂SO₃ + 2HCl
  • Thionyl chloride hydrolyzes to give sulfurous acid (H₂SO₃).

Therefore, the correct answer is: (B) H₃PO₄, NH₃, and H₂SO₃

CONCEPT:

Reaction of Calcium Carbide with Water

• Calcium carbide (CaC₂) reacts vigorously with water to produce acetylene gas (C₂H₂) and calcium hydroxide (Ca(OH)₂).
• The reaction is represented by the following chemical equation:

  CaC₂ + 2H₂O → C₂H₂ + Ca(OH)₂

EXPLANATION:

• When calcium carbide comes into contact with water, the carbide ion (C^2-) reacts with water molecules to form acetylene (C₂H₂) gas.
• Acetylene is an alkyne (hydrocarbon) characterized by a triple bond between its two carbon atoms. It is widely used as a fuel and a precursor in chemical synthesis.
• The other product of the reaction, calcium hydroxide (Ca(OH)₂), is a solid and remains in the reaction mixture.
• This reaction is highly exothermic and produces acetylene gas vigorously, which is why calcium carbide is handled with care.

Therefore, the correct answer is Option 3: Acetylene.

CONCEPT:

Hybridisation in Graphite

• Hybridisation refers to the mixing of atomic orbitals to form new hybrid orbitals that can form covalent bonds.
• Graphite is a crystalline form of carbon where each carbon atom is bonded to three other carbon atoms in a planar hexagonal arrangement.
• The hybridisation of carbon atoms in graphite is sp².
• In sp² hybridisation:
  • One s orbital and two p orbitals mix to form three sp² hybridised orbitals.
  • The three hybrid orbitals lie in the same plane at an angle of 120°, forming a trigonal planar geometry.
  • The unhybridised p orbital is perpendicular to the plane and forms delocalised π bonds, giving graphite its characteristic electrical conductivity.

EXPLANATION:

• In graphite:
  • Each carbon atom forms three sigma (σ) bonds with neighboring carbon atoms using sp² hybridised orbitals.
  • The unhybridised p orbital of each carbon atom overlaps with the unhybridised p orbitals of adjacent carbon atoms, forming a delocalised π-electron system.
  • This delocalisation contributes to graphite’s good electrical conductivity and its layered structure.
• sp³ hybridisation (option 1) occurs in tetrahedral structures like diamond, not in graphite.
• sp hybridisation (option 3) is found in linear molecules like acetylene (C₂H₂).
• sp³ and sp hybridisation together (option 4) do not occur in graphite.

Therefore, the correct answer is option 2: sp² hybridisation.

CONCEPT:

Shielding Effect of Electrons

• The shielding effect, also known as the screening effect, refers to the reduction in the effective nuclear charge experienced by an electron in a multi-electron atom due to repulsion by other electrons.
• Electrons in inner shells shield electrons in outer shells from the full attractive force of the nucleus.
• The extent of shielding depends on the type of orbital the electron occupies (s, p, d, or f). This is because the shape and penetration of the orbitals influence their ability to shield other electrons.
• The order of shielding effectiveness is determined by the proximity and penetration of the orbitals relative to the nucleus.

EXPLANATION:

• The shielding effect follows the order:
  • s > p > d > f
• Reasoning behind this order:
  • s orbitals: Spherical and closest to the nucleus, they have the highest penetration and are most effective at shielding.
  • p orbitals: Less penetration than s orbitals but still shield effectively.
  • d orbitals: More diffuse and farther from the nucleus, so they are less effective at shielding compared to s and p orbitals.
  • f orbitals: Most diffuse and located farthest from the nucleus, making them the least effective at shielding.

Therefore, the correct decreasing order of the shielding effect of electrons is Option 4: s > p > d > f.

The correct answer is Nitric acid.

• Nitric acid is used in the purification of gold and silver.

Key Points

• Nitric acid is used in the purification of gold. The acid mixture aqua regia, or royal water, dissolves gold and is used to purify scrap alloy containing gold.
  • Aqua regia is a mixture of hydrochloric acid and nitric acid in a 3:1 ratio.
  • Nitric acid is a nitrogen oxoacid of formula HNO3 in which the nitrogen atom is bonded to a hydroxy group and by equivalent bonds to the remaining two oxygen atoms.

Important Points

The correct answer is Next to diamond, graphite is the second hardest known substance.

Key Points

• Allotropes of carbon:
  • Carbon allotropes refer to different well-defined structures of carbon-pure materials, in which carbon atoms are bonded in specific ways.
  • Carbon shows allotropic forms like Diamond, graphite, Fullerene.
    • Graphite:
      • Graphite is a good conductor of heat and electricity.
      • It is very soft and slippery and for this reason, graphite is used as a lubricant in the machine running at high temperatures, where oil cannot be used as a lubricant.
      • Every carbon atom in graphite is bonded to three other carbon atoms in such a way that a layered hexagonal structure is formed.
    • Diamond:
      • Diamond has a high density of 3.51 gm due to its three-dimensional giant structure.
      • It is a bad conductor of electricity.
      • Diamond is the hardest substance on earth.
      • It is used as an abrasive for sharpening hard tools.
    • Fullerenes are used as conductors.
      • It can be used as an absorber of gases.
      • Fullerenes are used as lubricants.
      • Some forms of fullerenes are used in making cosmetics-related ingredients.

Key Points

• Allotrope: The different structure of same chemical compound is called Allotrope.
• Buckminister fullerene is a stable structure of 60 carbon atoms.
• It is also known as Buckyball or just C60.
• The structure has 12 Pentagon rings and 20 hexagon rings.
• The structure is very strong and stable.

Additional Information

Other allotropes of Carbon are

• It is a hard, beautiful, crystalline allotrope of carbon.
• In an atom, each carbon atom is linked to four neighbouring carbon atoms.
• These have tetrahedral three-dimensional symmetry.
• Diamond doesn't have free electrons. So. it is a non-conductor of electricity.
• Diamond is a precious stone used in jewellery.

Graphite-

• It is a soft greyish black crystalline substance.
• It was discovered in 1795 by scientist 'Nicholas Jacques Conte'.
• Its's density is 1.9 to 2.3 g/cm3.
• Each carbon atom is attached to three other carbon atoms forming a 'Hexagonal planar structure'.
• Free electrons move through the layers of graphite, so graphite is a good conductor of electricity.

• In a diamond, the carbon atoms are arranged tetrahedrally.
• 98Each carbon atom is attached to four other carbon atoms 1.544 x 10-10 meters away with a C-C-C bond angle of 109.5 degrees.
• The structure is given as follows:

• It is a strong, rigid three-dimensional structure that results in an infinite network of atoms.

• This accounts for the diamond's hardness, extraordinary strength, and durability and gives the diamond a higher density than graphite (3.514 grams per cubic centimeter). Because of its tetrahedral structure, diamond also shows great resistance to compression.

The correct answer is Diamond.

Key Points

• Diamond is the hardest substance on Earth.
• It has carbon atoms with four covalent bonds (four valence electrons is connected with four other carbon atoms).
• Diamond is the purest form of carbon.
• It is a non-metal that reflects light.
• It is a good insulator(bad conductor) of heat and electricity.
• It is used to drill rocks and to cut glasses.
• Diamond has a high density and high refractive index of 2.415.

Important Points

Allotropes

Substances with the same chemical properties but different physical properties are called allotropes.

Some of the allotropes of carbon are

• Diamond
• Graphite
• Buckminsterfullerene
• Charcoal

Additional Information

Buckminsterfullerene

It is a crystalline form of carbon.

• It was named after an American architect, Buckminster fuller.
• It consists of 60 carbon atoms joined to form a spherical molecule similar to a soccer ball. 
• The formula of 'Buckminsterfullerene' is C60.

Graphite

• It is chemically more reactive than diamond.
• It is a good conductor (bad insulator) of heat and electricity.
• Graphite has a hexagonal structure held by weak Vander Waal's force.

Uses:

• It is used as an electrode in furnaces.
• In a nuclear reactor, graphite is used as a moderator.
• It helps as a reducing agent in the steel manufacturing industry.

Iron

• Iron is the metal present in group 8 of the periodic table.
• Iron combined with nickel and chromium forms stainless steel.
• Wrought iron is known as the purest form of iron.
• In 2021, Karnataka became the largest producer of iron ore in India.​​

The correct answer is Carbonic Acid.

• When carbon dioxide dissolves in water it gives Carbonic Acid.

Key Points

• When carbon dioxide dissolves in water it gives carbonic acid which can then become bicarbonate.
• This is how the carbonic acid shuttled around the body during aerobic respiration. 
• Carbonic acid, (H₂CO₃), a compound of the elements hydrogen, carbon, and oxygen.
  • It is formed in small amounts when its anhydride, carbon dioxide (CO₂), dissolves in water.
  • Carbonic acid plays a role in the assembly of caves and cave formations like stalactites and stalagmites.
  • Carbonic acid is widely used in the production of soft drinks, artificially carbonated sparkling wines, and other bubbly beverages.
  • Carbonic acid salts are called bicarbonates (or carbonates of hydrogen), and carbonates.

Additional Information

• Citric acid is an organic compound with the chemical formula HOC(CO2H)(CH2CO2H)2.
  • Usually encountered as a white solid, it is a weak organic acid. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in the metabolism of all aerobic organisms.
• Sulfuric acid or sulphuric acid, also known as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, and hydrogen, with the molecular formula H₂SO₄.
  • It is a colourless, odourless, and viscous liquid that is miscible with water.
• Acetic acid, systematically named ethanoic acid, is an acidic, colourless liquid and organic compound with the chemical formula CH₃COOH.
  • Vinegar is no less than 4% acetic acid by volume, making acetic acid the main component of vinegar apart from water.
  • Acetic acid is the second simplest carboxylic acid.

Key Points

• All the elements of the group 15 elements form tri oxides and pentoxides having the general formula M₂O₃ or M₂O₅.
• The oxides of Nitrogen, Phosphorus, and Arsenic are acidic.
• The trioxide of antimony Sb2O3 is amphoteric while that of bismuth Bi2O3 is basic.
• As2O3 is acidic in nature.
• The pentoxides of all these elements are acidic but acidic character decreases down the group.
• Thus, P₂O₅ is the strongest acidic oxide whereas Bi₂O₃  is the weakest acidic oxide.
• The acidic character of the same element increases with an increase in the oxidation state.

Hence, the most acidic oxide among the following is P2O5.

​Important Points

Facts about P₂O₅:

•  It is also written as P₄O₁₀ and is called phosphorus pentoxide.
• It is prepared by burning phosphorus in excess of air or oxygen. It is a white solid which sublimes on heating.
• It is a strong dehydrating agent and dehydrates nitric acid as well as sulphuric acid.
• The structure is:

​

Additional Information

• N₂O₅ is the most acidic of group 15 elements. 

The correct answer is CO + N₂

• Producer gas is a mixture of CO + N₂

Key Points

• Producer gas:
  • A typical producer gas obtained from coke contains 27% carbon monoxide, 12% hydrogen, 0.5% methane, 5% carbon dioxide and 55% nitrogen, by volume.
  • Producer gas is fuel gas that is made from material such as coal.
  • A combustible mixture of nitrogen, carbon monoxide, and hydrogen gives the producer gas. 
  • It is the cheapest gaseous fuel; however, its calorific value is not very high because it has a large proportion of nitrogen.
  • It is made by the partial combustion of carbonaceous substances usually coal, in an atmosphere of air and steam. 

Additional Information

• Coal gas is a mixture of H₂, CH₄, CO, and gases like N₂, C₂, H₄, O₂, etc. 
• Oil gas is a mixture of H₂, CH₄, C₂H₄, CO, and other gases like CO₂.
• Syngas, or synthesis gas, is a fuel gas mixture consisting primarily of hydrogen, carbon monoxide, and very often some carbon dioxide. 

The correct answer is Sea.

Key Points

• Out of the options, the greatest source of halogens is Sea.
  • Halogens are a group of elements in the periodic table that include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).
  • These elements are very reactive and don't often occur in their pure form in nature.
  • Instead, they are commonly found combined with other elements, predominantly as salts dissolved in seawater.
  • Seawater: Contains large amounts of dissolved salts, including sodium chloride (NaCl), magnesium chloride (MgCl₂), and potassium chloride (KCl).
    • These salts release chloride (Cl) and, to a lesser extent, bromide (Br) and iodine (I) when dissolved in water.

Additional Information

• Lake water: While it also contains dissolved salts, the concentration of halogens in lakes is generally much lower than in seawater.
• Emissions from automobiles: Although car exhaust might contain trace amounts of certain halogens like chlorine from combustion or brake pads, it's not a significant source compared to the vast reservoirs in seawater.
• Facts about halogens:
  • They play crucial roles in various biological processes, like thyroid function in humans.
  • Some halogens have industrial applications, like chlorine in disinfecting water and bromine in flame retardants.
  • Due to their high reactivity, halogens can also be harmful if not handled properly.

Concept:

Carbon-carbon bond length is maximum in diamond because the diamond has a purely single bond.

The carbon atoms are held by strong covalent bonds and are arranged in a three-dimensional tetrahedral structure. Due to which diamond is hard. All the C-C bond are of the same length is 1.54 nm. In this rigid network, none of the carbon atoms can move. This accounts for the fact that diamonds are so hard and have such a high melting point.

While graphite, C₇₀ (fullerene), and C₆₀ (Buckminsterfullerene) single and partial double bonds.