CBSE Class 11 Chemistry HOTs Structure of Atom

Question. The potential energy of electron present in ground state of Li²⁺ ion is represented by :
(a) +3e²/4π∈₀r
(b) -3e/4π∈₀r
(c) -3e²/4π∈₀r²
(d) -3e²/4π∈₀r
Answer : D

Question. An electron in the ground state of hydrogen was excited to a higher energy level using monochromatic radiations of wave length (λ) 975
Å. The longest wave length that appears in the resulting spectrum is due to transition from:
(a) n₄ → n₁
(b) n₄ → n₃
(c) n₅ → n₄
(d) n₅ → n₁
Answer : B

Question. Which of the following pairs of nucleides are isodiaphers ?
(a) ¹³₆C and ¹⁶₈O
(b) ¹₁H and ²₁H
(c) ³₁H and 4₂He
(d) ⁵⁵₂₅Mn ⁶⁵₃₀and Zn
Answer : D

Question. Based on equation E = – 2.178 × 10^-18 J (Z²/n²) certain conclusions are written. Which of them is not correct ?
(a) Larger the value of n, the larger is the orbit radius.
(b) Equation can be used to calculate the change in energy when the electron changes orbit.
(c) For n = 1, the electron has a more negative energy than it does for n = 6 which mean that the electron is more loosely bound in the smallest allowed orbit.
(d) The negative sign in equation simply means that the energy or electron bound to the nucleus is lower than it would be if the electrons were at the infinite distance from the nucleus.
Answer : C

Question. The velocity of an electron in excited state of Hatom is 1.093 x 10⁶ m/s. What is the circumference of this orbit?
(a) 3.32 x 10^–10 m
(b) 6.64 x 10^–10 m
(c) 13.30 x 10^–10 m
(d) 13.28 x 10^–10 m
Answer : C

Question. For Balmer series in the spectrum of atomic hydrogen, the wave number of each line is given by v¯ = RH (1/n₁² - 1/n₂²) where RH is a constant and n₁ and n₂ are integers. Which of the following statement(s) is (are) correct?
I. As wavelength decreases, the lines in the series converge.
II. The integer n₁ is equal to 2.
III. The ionization energy of hydrogen can be calculated from the wave number of these lines.
IV. The line of longest wavelength corresponds to n₂ = 3.
(a) I, II and III
(b) II, III and IV only
(c) I, II and IV
(d) II and IV only
Answer : C

Question. If m and e are the mass and charge of the revolving electron in the orbit of radius r for hydrogen atom, the total energy of the revolving electron will be:
(a) 1 e²/2 r
(b) e²/r
(c) me²/r
(d) 1 e²/2 r
Answer : D

Question. What transition in He+ ion shall have the same wave number as the first line in Balmer series of H atom?
(a) 7 → 5
(b) 6 → 4
(c) 5 → 3
(d) 4 → 2
Answer : B

Question. Let m_p be the mass of a proton, mn that of a neutron, M₁ that of a ²⁰₁₀Ne nucleus and M₂ that of a ⁴⁰₂₀Ca nucleus. Then
(a) M₂ = 2M₁
(b) M₁ < 10(mp + mn)
(c) M₂ > 2M₁
(d) M₁ = M₂
Answer : A

Question. The correct representation of wavelength intensity relationship of an ideal black body radiation at two different temperatures T₁ and T₂ is

Answer : A

Question. Among the following, the incorrect statement is
(a) No two electrons in an atom can have the same set of four quantum numbers
(b) The maximum number of electrons in the shell with principal quantum number, n is equal to n² + 2
(c) Electrons in an orbital must, have opposite spin
(d) In the ground state, atomic orbitals are filled in the order of their increasing energies
Answer : B

Question. Calculate the minimum and maximum number of electrons which may have magnetic quantum number, m = +1 and spin quantum number, s = - (1/2) in chromium (Cr):
(a) 0, 1
(b) 1, 2
(c) 4, 6
(d) 2, 3
Answer : D

Question. The electrons, identified by quantum numbers n and l,
(I) n = 3, l = 2            (II) n = 5, l = 0
(III) n = 4, l = 1         (IV) n = 4, l = 2
(V) n = 4, l = 0 can be placed in order of increasing energy, as
(a) I < V < III < IV < II
(b) I < V < III, II, IV
(c) V < I < III < II < IV
(d) V < I < II < III < IV
Answer : B

Question. The angular momentum of an electron in a Bohr’s orbit of He⁺ is 3.1652 × 10^–34 kg-m²/sec. What is the wave number in terms of Rydberg constant (R) of the spectral line emitted when an electron falls from this level to the first excited state. [Use h = 6.626 x 10^–34 J × s]
(a) 3R
(b) 5R/9
(c) 3R/4
(d) 8R/9
Answer : B

Question. A electron in a hydrogen atom in its ground state absorbs 1.5 times as much energy as the minimum required for it to escape from the atom. What is the velocity of the emitted electron?
(a) 1.54 x 10⁶ m/s
(b) 1.54 x 10⁸ m/s
(c) 1.54 x 10³ m/s
(d) 1.54 x 10⁴ m/s
Answer : A

Question. For a multi-electron atom, the highest energy level among the following is
(a) n = 5, l = 0, m = 0, s = +½
(b) n = 4, l = 2, m = 0, s = +½
(c) n = 4, l = 1, m = 0, s = +½
(d) n = 5, l = 1, m = 0, s = +½
Answer : D

Question. The energies E₁ and E₂ of two radiations are 25 eV and 50 eV, respectively. The relation between their wavelengths i.e., λ₁ and λ₂ will be :
(a) λ₁ = λ₂
(b) λ₁ = 2λ₂
(c) λ₁ = 4λ₂
(d) λ₁ = (1/2)λ₂
Answer : B

Question. Among the following, the correct statement about cathode ray discharge tube is
(a) the electrical discharge can only be observed at high pressure and at low voltages.
(b) in the absence of external electrical or magnetic field, cathode rays travel in straight lines.
(c) the characteristics of cathode rays depend upon the material of electrodes.
(d) the characteristics of cathode rays depend upon the gas present in the cathode ray tube.
Answer : B

Question. The correct order of energy of 2s-orbitals in H, Li, Na and K, is
(a) K < Na < Li < H
(b) Na < Li < K < H
(c) Na < K < H < Li
(d) H < Na < Li < K
Answer : A

Question. Which of the following radial distribution graphs correspond to l = 2 for the H atom ?

Answer : C

Question. A 600 W mercury lamp emits monochromatic radiation of wavelength 331.3 nm. How many photons are emitted from the lamp per second? h = 6.62 × 10^–34 Js velocity of light = 3 × 10⁸ ms^–1
(a) 1.0 × 10¹⁹
(b) 1.0 × 10²³
(c) 1.0 × 10²¹
(d) 2.0 × 10²³
Answer : C

Numeric Value Answer

Question. An electron has a speed of 30,000 cm sec^–1 accurate upto 0.001%. What is the uncertainty in locating it’s position.
Answer : 2

Question. Determine the Bohr orbit of Li²⁺ ion in which electron is moving at speed equal to the speed of electron in the first Bohr orbit of H-atom.
Answer : 3

Question. An electron with de Broglie wavelength 4 × 10^–6 m makes transition to a state with de Broglie wavelength 6 × 10^–6 m. The wavelength of photon generated is mc/h X x10^-11 m. What is the value of x?
Answer : 576

Question. Calculate the ratio of wavelength of first line of Balmer series of H-atom to the wavelength of first line of Lyman series of 10 times ionized sodium atom.
Answer : 653.4

Question. The energy of the electron in the second and the third Bohr’s orbits of the hydrogen atom is – 5.42 × 10^–12 erg and –2.41 × 10^–12 erg respectively.
Calculate the wavelength of the emitted radiation when the electron drops from the third to the second orbit.
Answer : 6.604

Question. What is the sum of radial node(s) and nodal plane(s) for 4d_z^2–orbital?
Answer : 1

Question. A hydrogen atom with an electron in the first shell absorbs ultraviolet light with a wavelength of 1.03 × 10^–7 m. To what shell does the electron jump?
Answer : 3

Question. If the energies of two radiations of wavelength 800 nm and 400 nm are E₁ and E₂ respectively. Then calculate the value of E₂/E₁.
Answer : 2

Question. To stop the flow of photoelectrons produced by electromagnetic radiation incident on a certain metal, a negative potential of 300 V is required. If the photoelectric threshold of metal is 1500 Å, what is the frequency of the incident radiation (in terms of 10¹⁶ Hz)?
Answer : 7.45

Question. Naturally occurring boron consists of two isotopes whose atomic weights are 10.01 and 11.01. The atomic weight of natural boron is 10.81. Calculate the percentage of isotope with atomic weight 11.01 in natural boron.
Answer : 80