Here are 50 Assertion and Reason questions based on Chapter 7: The p-Block Elements from the NCERT Class 12 Chemistry book, complete with answer options, questions, and detailed explanations.
(1) Both Assertion and Reason are correct, and Reason is the correct explanation
of Assertion.
(2) Both Assertion and Reason are correct, but Reason is not the correct
explanation of Assertion.
(3) Assertion is correct, but Reason is incorrect.
(4) Assertion is incorrect, but Reason is correct.
Reason (R): Noble gases have a stable electronic configuration with a complete octet, which makes them chemically inert.
Answer: (1)
Explanation: Noble gases have completely filled outer shells,
making them highly stable and chemically inert. The reason explains the
assertion.
Reason (R): Chlorine in +1 oxidation state has a tendency to accept electrons and get reduced to a lower oxidation state.
Answer: (1)
Explanation: Chlorine in the +1 oxidation state acts as an
oxidizing agent by accepting electrons, which is explained in the reason.
Reason (R): Ammonia exhibits hydrogen bonding, while nitrogen does not.
Answer: (1)
Explanation: Ammonia has hydrogen bonding between its
molecules, leading to stronger intermolecular forces and a higher boiling point
compared to nitrogen.
Reason (R): Nitrogen has multiple oxidation states, allowing it to form various compounds with oxygen.
Answer: (1)
Explanation: Nitrogen has oxidation states ranging from -3 to
+5, enabling it to form several oxides such as N2O, NO, NO2, and N2O5.
Reason (R): Fluorine's small size and high nuclear charge make it capable of attracting electrons more strongly than any other element.
Answer: (1)
Explanation: Fluorine's high electronegativity is due to its
small atomic size and high effective nuclear charge, which allow it to attract
electrons strongly.
Reason (R): Boron, being an electron-deficient element, does not achieve a full octet in its compounds.
Answer: (1)
Explanation: Boron in BF3 has only six electrons in its valence
shell, forming an electron-deficient structure. This is explained in the reason.
Reason (R): Oxygen is smaller in size compared to sulfur, which enables it to attract electrons more strongly.
Answer: (1)
Explanation: Oxygen is smaller than sulfur and has a higher
effective nuclear charge, which results in a greater tendency to attract
electrons.
Reason (R): White phosphorus exists as P4 molecules, which are highly reactive due to the presence of strained bonds.
Answer: (1)
Explanation: White phosphorus has P4 molecules where the bonds
are strained and unstable, making it highly reactive.
Reason (R): As we move down the group, the atomic size increases, which weakens the attraction between the nucleus and the bonding electrons.
Answer: (1)
Explanation: The increase in atomic size down the halogen group
reduces the effective nuclear charge on the valence electrons, leading to lower
electronegativity.
Reason (R): With an increase in atomic size down the group, the outermost electrons are farther from the nucleus and are less tightly held.
Answer: (1)
Explanation: The larger atomic size and weaker attraction
between the nucleus and valence electrons make it easier to remove an electron
as we move down the group.
Reason (R): The increase in atomic size and molecular mass leads to stronger van der Waals forces, which require more energy to overcome.
Answer: (1)
Explanation: As the halogen molecules become larger and
heavier, the van der Waals forces between them become stronger, raising their
melting and boiling points.
Reason (R): Nitrogen has a strong N≡N bond in its molecular form, which makes it less reactive compared to phosphorus.
Answer: (1)
Explanation: The strong triple bond in nitrogen (N≡N) makes it
more stable and less reactive compared to phosphorus, which has weaker bonds in
its allotropes.
Reason (R): The lone pairs on oxygen repel the bonding pairs, causing the bond angle to be smaller than the tetrahedral angle of 109.5°.
Answer: (1)
Explanation: The presence of lone pairs on oxygen results in a
bond angle smaller than the tetrahedral angle, leading to a bond angle of
104.5°.
Reason (R): In PCl5, phosphorus forms five bonds, which requires the involvement of one s, three p, and one d orbital.
Answer: (1)
Explanation: The five bonds in PCl5 are formed by sp3d
hybridization, which involves one s, three p, and one d orbital.
Reason (R): Group 15 elements have half-filled p orbitals, which provide extra stability and make it harder to remove an electron.
Answer: (1)
Explanation: The half-filled p orbitals in Group 15 elements
provide extra stability, leading to higher ionization enthalpy compared to Group
14 elements.
Reason (R): HCl is an ionic compound, and water can dissolve ionic compounds due to its polarity.
Answer: (1)
Explanation: HCl dissolves in water, dissociating into H+ and
Cl− ions due to the polarity of water, which can stabilize the ions.
Reason (R): As we move across the period, the electronegativity of the elements increases, making their oxides more acidic.
Answer: (1)
Explanation: The increase in electronegativity across the
period leads to the formation of more acidic oxides, as the oxides are better
able to donate protons.
Reason (R): The ability to accept electrons decreases as we move down the group due to the increasing atomic size.
Answer: (1)
Explanation: As the atomic size increases, the nuclear charge
becomes less effective at attracting electrons, reducing the oxidizing power of
halogens.
Reason (R): The smaller size of nitrogen leads to a stronger bond between nitrogen atoms, resulting in a shorter bond length.
Answer: (1)
Explanation: The shorter bond length in nitrogen is due to its
smaller size, which results in stronger overlap of the atomic orbitals and a
shorter bond length compared to phosphorus.
Reason (R): Noble gases have a stable octet configuration, requiring more energy to remove an electron compared to halogens.
Answer: (1)
Explanation: Noble gases have a stable electronic
configuration, which requires higher energy to remove an electron compared to
halogens, which are one electron short of a complete octet.
Reason (R): Oxygen has a smaller size and higher electronegativity than sulfur, which allows it to form more stable oxides.
Answer: (1)
Explanation: Oxygen, due to its small size and high
electronegativity, forms a greater variety of stable oxides compared to sulfur.
Reason (R): Fluorine is smaller than chlorine, leading to a smaller fluoride ion.
Answer: (1)
Explanation: Fluorine has a smaller atomic size compared to
chlorine, resulting in a smaller fluoride ion.
Reason (R): Halogens have high electronegativity, which makes them readily accept electrons to form negative ions.
Answer: (1)
Explanation: Halogens have a high electron affinity, meaning
they readily accept electrons, making their electron affinity negative
(exothermic process).
Reason (R): Boron in BF3 has only six electrons in its valence shell, forming an incomplete octet.
Answer: (1)
Explanation: Boron in BF3 has only six valence electrons,
making the compound electron-deficient.
Reason (R): Oxides with higher oxidation states are more acidic due to their higher ability to accept electrons.
Answer: (1)
Explanation: Higher oxidation states lead to more acidic
oxides, as the metal cation has a greater ability to polarize the oxide ion and
donate protons.
Reason (R): Group 15 elements have relatively high electronegativity and small atomic size, which favors covalent bonding.
Answer: (1)
Explanation: The high electronegativity and small size of Group
15 elements make it easier for them to form covalent bonds rather than ionic
bonds.
Reason (R): Nitrogen is a smaller molecule with weaker van der Waals forces compared to phosphorus, leading to a lower boiling point.
Answer: (1)
Explanation: Due to the smaller molecular size of nitrogen and
weaker intermolecular forces, it has a lower boiling point than phosphorus,
which is larger and has stronger van der Waals forces.
Reason (R): Fluorine is smaller in size and has a higher electronegativity compared to chlorine, making it more reactive.
Answer: (1)
Explanation: The small size and high electronegativity of
fluorine allow it to react more readily than chlorine, which has a larger atomic
size and lower electronegativity.
Reason (R): Ozone contains a higher concentration of oxygen in an excited state, making it more reactive and a stronger oxidizing agent than molecular oxygen.
Answer: (1)
Explanation: Ozone (O₃) has a higher tendency to donate oxygen
atoms and oxidize other substances, which makes it a stronger oxidizing agent
than O₂.
Reason (R): The atomic size increases down the group, and as a result, the ability to attract electrons decreases.
Answer: (1)
Explanation: The halogens show decreasing reactivity down the
group due to the increasing atomic size and decreasing electron affinity, which
reduces their ability to gain electrons.
Reason (R): Phosphorus has the ability to form both +3 and +5 oxidation states in its compounds.
Answer: (1)
Explanation: In PCl3, phosphorus exhibits a +3 oxidation state,
which is common for phosphorus in its lower oxidation state, and it can also
form +5 oxidation state in compounds like PCl5.
Reason (R): Oxygen can form an O-O single bond due to its high electronegativity and ability to accept electrons.
Answer: (1)
Explanation: Oxygen in peroxides (like H₂O₂) forms an O-O bond,
which is due to its ability to form a weak bond with another oxygen atom,
creating a peroxide bond.
Reason (R): Boron has a relatively small atomic size and high ionization energy, which favors covalent bonding over ionic bonding.
Answer: (1)
Explanation: Boron’s small size and high ionization energy make
it more likely to form covalent bonds, which is why it forms many covalent
compounds.
Reason (R): Chlorine in ClF₃ has a higher oxidation state due to the high electronegativity of fluorine.
Answer: (1)
Explanation: Chlorine in ClF₃ has an oxidation state of +3,
which is higher than the oxidation state of 0 in Cl₂, due to the higher
electronegativity of fluorine compared to chlorine.
Reason (R): The ability of phosphorus to form multiple allotropes is due to its ability to form different types of bonds.
Answer: (1)
Explanation: Phosphorus exists in several allotropes (e.g.,
white, red, and black phosphorus) due to its ability to form different types of
bonds, including covalent and network covalent.
Reason (R): Fluorine is more electronegative than oxygen, leading to a stronger dipole-dipole interaction in HF.
Answer: (1)
Explanation: The high electronegativity of fluorine in HF leads
to stronger hydrogen bonding compared to H2O, where oxygen is also
electronegative, but fluorine is more electronegative.
Reason (R): The presence of two lone pairs on chlorine results in the bond angle being less than the ideal value.
Answer: (1)
Explanation: The bond angle in ClF₃ is 87.5° due to the
repulsion caused by the two lone pairs on chlorine, which reduces the bond angle
from the ideal value.
Reason (R): As the atomic size increases down the group, the ability to accept an electron decreases.
Answer: (1)
Explanation: The electron affinity decreases down the halogen
group because the larger atomic size weakens the attraction between the nucleus
and the incoming electron.
Reason (R): The increase in electronegativity of elements from left to right makes their oxides more acidic.
Answer: (1)
Explanation: As the electronegativity increases across a
period, the ability of the element to polarize the oxide ion increases, leading
to stronger acidic behavior of the oxides.
Reason (R): Graphite has strong covalent bonds between its layers, while diamond has a giant covalent structure with strong bonds throughout.
Answer: (4)
Explanation: This assertion is incorrect. Diamond has a higher
melting point than graphite due to its 3D covalent network structure, which
requires more energy to break.
Reason (R): The N≡N bond in nitrogen is weaker than the O=O bond in oxygen.
Answer: (4)
Explanation: This assertion is incorrect. The N≡N bond in
nitrogen is actually stronger than the O=O bond in oxygen, resulting in nitrogen
having a higher bond dissociation enthalpy.
Reason (R): Ozone is a more stable molecule than dioxygen.
Answer: (4)
Explanation: The assertion is incorrect. Ozone (O₃) is more
reactive than O₂ because it has a higher potential to react due to its unstable
structure.
Reason (R): Fluorine is highly electronegative and can form bonds with almost all elements.
Answer: (3)
Explanation: Fluorine can form bonds with most elements but not
with noble gases like helium, neon, and argon, as these elements already have a
stable electron configuration.
Reason (R): Nitrogen has a stable N≡N bond, which makes it less reactive than phosphorus.
Answer: (1)
Explanation: The strong N≡N bond makes nitrogen less reactive
than phosphorus, which has weaker bonds in its molecular form.
Reason (R): Nitrogen in nitric acid (HNO₃) is bonded to three oxygen atoms, two of which are doubly bonded.
Answer: (1)
Explanation: Nitrogen in HNO₃ has an oxidation state of +5,
consistent with the fact that it is bonded to three oxygen atoms with one single
bond and two double bonds.
Reason (R): HF forms stronger hydrogen bonds than HCl.
Answer: (1)
Explanation: HF has stronger hydrogen bonding compared to HCl,
leading to a higher boiling point.
Reason (R): As the atomic size increases, the ionization enthalpy decreases, making it easier for atoms to lose electrons.
Answer: (1)
Explanation: As we move down a group, the atomic size increases
and ionization enthalpy decreases, enhancing metallic character.
Reason (R): As the atomic size increases down the group, the ability to attract electrons decreases.
Answer: (1)
Explanation: As atomic size increases, the attraction between
the nucleus and bonding electrons weakens, reducing electronegativity.
Reason (R): Halogens are highly electronegative, which allows them to accept electrons readily.
Answer: (1)
Explanation: Halogens have the highest electron affinity due to
their high electronegativity and small atomic size, which allows them to attract
electrons effectively.
Reason (R): Nitrogen has a small size and a high ionization enthalpy, which allows it to stabilize higher oxidation states.
Answer: (1)
Explanation: Nitrogen can form a stable +5 oxidation state in
compounds like HNO₃ due to its high ionization enthalpy and the ability to
stabilize the oxidation state.