Chapter 2: Structure of Atom Assertion-Reason Questions | chemistry Class 11 CBSE

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 1

Logic Check

Assertion (A): The characteristics of cathode rays (electrons) do not depend on the material of the electrodes or the nature of the gas in the cathode ray tube. Reason (R): Electrons are basic constituents of all atoms and are identical regardless of their source.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 2

Logic Check

Assertion (A): In Rutherford's alpha-particle scattering experiment, most alpha particles passed through the gold foil undeflected. Reason (R): Most of the space inside an atom is occupied by the positively charged nucleus.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 3

Logic Check

Assertion (A): Isotopes of an element show the same chemical behaviour. Reason (R): Chemical properties of atoms are controlled by the number of electrons, which is determined by the number of protons (atomic number), not by the number of neutrons.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 4

Logic Check

Assertion (A): The energy of an electron in the hydrogen atom becomes more negative as n decreases. Reason (R): A more negative energy value means the electron is more tightly bound to the nucleus and the atom is more stable.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 5

Logic Check

Assertion (A): Red light of any intensity cannot cause the photoelectric effect in potassium metal (threshold frequency ν₀ = 5.0 × 10^14 Hz), even though red light has frequency ~4.5 × 10^14 Hz. Reason (R): The kinetic energy of ejected electrons increases with the intensity of incident light.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 6

Logic Check

Assertion (A): The de Broglie wavelength of a moving cricket ball is not observable experimentally. Reason (R): The wavelength of macroscopic objects is immeasurably small due to their large mass, making wave behaviour undetectable.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 7

Logic Check

Assertion (A): Bohr's model of the hydrogen atom successfully explains the line spectrum of helium. Reason (R): Bohr's model can be applied to any atom by substituting the appropriate atomic number Z in the energy formula.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 8

Logic Check

Assertion (A): The 4s orbital fills before the 3d orbital during the building up of electronic configurations. Reason (R): The (n+l) value for 4s (n+l = 4) is lower than that for 3d (n+l = 5), so 4s has lower energy than 3d in neutral atoms.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 9

Logic Check

Assertion (A): Pauli's exclusion principle allows a maximum of two electrons in any atomic orbital. Reason (R): The two electrons in the same orbital must have opposite spin quantum numbers (+½ and −½), giving them different sets of four quantum numbers.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 10

Logic Check

Assertion (A): The 2s and 2p orbitals in hydrogen have the same energy. Reason (R): In hydrogen (one-electron system), orbital energy depends only on the principal quantum number n, not on the azimuthal quantum number l.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 11

Logic Check

Assertion (A): The Heisenberg uncertainty principle is significant only for microscopic particles like electrons, not for macroscopic objects. Reason (R): The product Δx × Δp ≥ h/4π involves Planck's constant h = 6.626 × 10^-34 J·s, which is extremely small; for large masses, the resulting uncertainties are negligible.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 12

Logic Check

Assertion (A): All s-orbitals are spherical in shape. Reason (R): For s-orbitals (l=0), the magnetic quantum number ml can only be 0, meaning there is no preferred spatial orientation.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 13

Logic Check

Assertion (A): Chromium (Z=24) has the electronic configuration [Ar]3d⁵4s¹ rather than [Ar]3d⁴4s². Reason (R): A half-filled 3d subshell (3d⁵) has extra stability due to symmetrical distribution of electrons and maximum exchange energy.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 14

Logic Check

Assertion (A): Emission spectra of atoms in the gas phase consist of discrete lines at specific wavelengths. Reason (R): Atoms can emit radiation of any frequency continuously when they return from excited states to lower energy states.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 15

Logic Check

Assertion (A): The number of angular nodes in a 3d orbital is 2. Reason (R): The number of angular nodes for any orbital equals the azimuthal quantum number l.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 16

Logic Check

Assertion (A): Light exhibits wave-particle duality. Reason (R): The wave nature of light explains diffraction and interference, while the particle nature (photons) explains the photoelectric effect and black body radiation.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 17

Logic Check

Assertion (A): Bohr's model cannot explain the stability of atoms other than hydrogen. Reason (R): Bohr's model correctly accounts for the wave character of electrons in all atoms.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 18

Logic Check

Assertion (A): The probability density |Ψ|² for the 1s orbital of hydrogen is maximum at the nucleus (r=0). Reason (R): The electron in the 1s orbital is most likely to be found at r=0 (at the nucleus).

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 19

Logic Check

Assertion (A): The Balmer series is the only series of hydrogen spectrum visible to the naked eye. Reason (R): The Balmer series corresponds to electron transitions ending at n=2, producing photons with wavelengths in the range 400–750 nm (visible light).

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 20

Logic Check

Assertion (A): Hund's rule states that electrons pair up in degenerate orbitals as soon as one electron enters the subshell. Reason (R): Pairing of electrons in degenerate orbitals is energetically unfavourable because paired electrons experience extra repulsion compared to electrons in separate orbitals.

Reasoning Options

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Chapter sections

Chapter 2: Structure of Atom | Assertion-Reason

Assertion (A): The characteristics of cathode rays (electrons) do not depend on the material of the electrodes or the nature of the gas in the cathode ray tube. Reason (R): Electrons are basic constituents of all atoms and are identical regardless of their source.

Assertion (A): In Rutherford's alpha-particle scattering experiment, most alpha particles passed through the gold foil undeflected. Reason (R): Most of the space inside an atom is occupied by the positively charged nucleus.

Assertion (A): Isotopes of an element show the same chemical behaviour. Reason (R): Chemical properties of atoms are controlled by the number of electrons, which is determined by the number of protons (atomic number), not by the number of neutrons.

Assertion (A): The energy of an electron in the hydrogen atom becomes more negative as n decreases. Reason (R): A more negative energy value means the electron is more tightly bound to the nucleus and the atom is more stable.

Assertion (A): Red light of any intensity cannot cause the photoelectric effect in potassium metal (threshold frequency ν₀ = 5.0 × 10^14 Hz), even though red light has frequency ~4.5 × 10^14 Hz. Reason (R): The kinetic energy of ejected electrons increases with the intensity of incident light.

Assertion (A): The de Broglie wavelength of a moving cricket ball is not observable experimentally. Reason (R): The wavelength of macroscopic objects is immeasurably small due to their large mass, making wave behaviour undetectable.

Assertion (A): Bohr's model of the hydrogen atom successfully explains the line spectrum of helium. Reason (R): Bohr's model can be applied to any atom by substituting the appropriate atomic number Z in the energy formula.

Assertion (A): The 4s orbital fills before the 3d orbital during the building up of electronic configurations. Reason (R): The (n+l) value for 4s (n+l = 4) is lower than that for 3d (n+l = 5), so 4s has lower energy than 3d in neutral atoms.

Assertion (A): Pauli's exclusion principle allows a maximum of two electrons in any atomic orbital. Reason (R): The two electrons in the same orbital must have opposite spin quantum numbers (+½ and −½), giving them different sets of four quantum numbers.

Assertion (A): The 2s and 2p orbitals in hydrogen have the same energy. Reason (R): In hydrogen (one-electron system), orbital energy depends only on the principal quantum number n, not on the azimuthal quantum number l.

Assertion (A): All s-orbitals are spherical in shape. Reason (R): For s-orbitals (l=0), the magnetic quantum number ml can only be 0, meaning there is no preferred spatial orientation.

Assertion (A): Chromium (Z=24) has the electronic configuration [Ar]3d⁵4s¹ rather than [Ar]3d⁴4s². Reason (R): A half-filled 3d subshell (3d⁵) has extra stability due to symmetrical distribution of electrons and maximum exchange energy.

Assertion (A): Emission spectra of atoms in the gas phase consist of discrete lines at specific wavelengths. Reason (R): Atoms can emit radiation of any frequency continuously when they return from excited states to lower energy states.

Assertion (A): The number of angular nodes in a 3d orbital is 2. Reason (R): The number of angular nodes for any orbital equals the azimuthal quantum number l.

Assertion (A): Light exhibits wave-particle duality. Reason (R): The wave nature of light explains diffraction and interference, while the particle nature (photons) explains the photoelectric effect and black body radiation.

Assertion (A): Bohr's model cannot explain the stability of atoms other than hydrogen. Reason (R): Bohr's model correctly accounts for the wave character of electrons in all atoms.

Assertion (A): The probability density |Ψ|² for the 1s orbital of hydrogen is maximum at the nucleus (r=0). Reason (R): The electron in the 1s orbital is most likely to be found at r=0 (at the nucleus).

Assertion (A): The Balmer series is the only series of hydrogen spectrum visible to the naked eye. Reason (R): The Balmer series corresponds to electron transitions ending at n=2, producing photons with wavelengths in the range 400–750 nm (visible light).

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