JEE Chemistry Structure Of Atom MCQs Set 09

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Chapter-wise Objective Questions: Structure Of Atom

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Multiple Choice Questions

Question 1: The qualitative difference between a 2s orbital and a 1s orbital is that the 2s orbital
(a) has one angular node
(b) has no node
(c) has one radial node
(d) is dumb-bell shaped
Show Answer & Explanation

Answer: (c) has one radial node

Explanation:
1. Radial nodes \(= n-l-1 = 2-0-1 = 1\); angular nodes \(= 0\)
2. A 1s orbital has no node.

Teacher's Note:
1. Count nodes using radial nodes = n - l - 1 and angular nodes = l. Remember the geometry: s is spherical, p has one nodal plane, and dz2 has a ring in the xy plane.

Question 2: The sum of the angular nodes and radial nodes of a 4d\(_{xy}\) orbital is
(a) 2
(b) 3
(c) 4
(d) 1
Show Answer & Explanation

Answer: (b) 3

Explanation:
1. Angular nodes \(= 2\); radial nodes \(= 4-2-1 = 1\)
2. Total \(= n-1 = 3\).

Teacher's Note:
1. Count nodes using radial nodes = n - l - 1 and angular nodes = l. Remember the geometry: s is spherical, p has one nodal plane, and dz2 has a ring in the xy plane.

Question 3: An orbital that has two radial nodes and two angular nodes is
(a) 5d
(b) 3d
(c) 4p
(d) 4f
Show Answer & Explanation

Answer: (a) 5d

Explanation:
1. Angular nodes = l = 2 means d
2. Radial nodes \(= n-2-1 = 2\) gives n = 5.

Teacher's Note:
1. Count nodes using radial nodes = n - l - 1 and angular nodes = l. Remember the geometry: s is spherical, p has one nodal plane, and dz2 has a ring in the xy plane.

Question 4: For similar orbitals with different values of n, the most probable distance of the electron from the nucleus
(a) decreases with n
(b) remains constant
(c) increases with n
(d) first increases and then decreases
Show Answer & Explanation

Answer: (c) increases with n

Explanation:
1. Higher shells are larger: the radial probability maximum moves out with increasing n.
2. Only option (c) agrees with this working.

Teacher's Note:
1. Count nodes using radial nodes = n - l - 1 and angular nodes = l. Remember the geometry: s is spherical, p has one nodal plane, and dz2 has a ring in the xy plane.

Question 5: Which of the following is true for the hydrogen atom?
(a) 3s has lower energy than 3p
(b) 3s, 3p and 3d orbitals have the same energy
(c) 3p has lower energy than 3d
(d) 3s and 3p are lower than 3d
Show Answer & Explanation

Answer: (b) 3s, 3p and 3d orbitals have the same energy

Explanation:
1. In a one-electron atom the energy depends only on n, so all orbitals of the same shell are degenerate.
2. Only option (b) agrees with this working.

Teacher's Note:
1. Count nodes using radial nodes = n - l - 1 and angular nodes = l. Remember the geometry: s is spherical, p has one nodal plane, and dz2 has a ring in the xy plane.

Question 6: The radial probability of finding an electron in a thin spherical shell of thickness dr at distance r is
(a) \(4\pi r^2\psi^2\,dr\)
(b) \(\pi r^2\psi^2\,dr\)
(c) \(2\pi r^2\psi^2\,dr\)
(d) \(\tfrac43\pi r^3\psi^2\,dr\)
Show Answer & Explanation

Answer: (a) \(4\pi r^2\psi^2\,dr\)

Explanation:
1. The shell volume is \(4\pi r^2dr\), and multiplying by the probability density \(\psi^2\) gives the probability.
2. Only option (a) agrees with this working.

Teacher's Note:
1. Count nodes using radial nodes = n - l - 1 and angular nodes = l. Remember the geometry: s is spherical, p has one nodal plane, and dz2 has a ring in the xy plane.

Question 7: Which of the following is NOT a characteristic of X-rays?
(a) They can ionise gases
(b) They are deflected by electric and magnetic fields
(c) They produce fluorescence on ZnS
(d) They have wavelengths shorter than ultraviolet
Show Answer & Explanation

Answer: (b) They are deflected by electric and magnetic fields

Explanation:
1. X-rays are uncharged electromagnetic waves, so fields do not deflect them.
2. Only option (b) agrees with this working.

Teacher's Note:
1. Count nodes using radial nodes = n - l - 1 and angular nodes = l. Remember the geometry: s is spherical, p has one nodal plane, and dz2 has a ring in the xy plane.

Question 8: The ground-state electronic configuration of the element with atomic number 56 is
(a) \([Xe]6s^2\)
(b) \([Xe]5d^2\)
(c) \([Kr]5s^25p^6\)
(d) \([Xe]4f^2\)
Show Answer & Explanation

Answer: (a) \([Xe]6s^2\)

Explanation:
1. 56 electrons: \([Xe]\) has 54, and the last two enter 6s (barium).
2. Only option (a) agrees with this working.

Teacher's Note:
1. For electrons in an atom, check the allowed ranges: l from 0 to n - 1, m from -l to +l and s = +1/2 or -1/2. For ions remove electrons from the outermost shell (4s) before 3d. Magnetic moment = sqrt(n(n+2)) B.M.

Question 9: The spin-only magnetic moment of an ion X\(^{n+}\) (Z = 26) is \(\sqrt{24}\) B.M. The number of unpaired electrons and the value of n are
(a) 2 and 4
(b) 3 and 1
(c) 0 and 2
(d) 4 and 2
Show Answer & Explanation

Answer: (d) 4 and 2

Explanation:
1. \(\sqrt{n(n+2)} = \sqrt{24}\) gives 4 unpaired electrons
2. Fe\(^{2+}\) (\(3d^6\)) has 4 unpaired electrons; Fe\(^{3+}\) has 5.

Teacher's Note:
1. For electrons in an atom, check the allowed ranges: l from 0 to n - 1, m from -l to +l and s = +1/2 or -1/2. For ions remove electrons from the outermost shell (4s) before 3d. Magnetic moment = sqrt(n(n+2)) B.M.

Question 10: Among Zn\(^{2+}\), Fe\(^{2+}\), Ni\(^{3+}\) and Cu\(^+\), the ion with the maximum number of unpaired electrons is
(a) Zn\(^{2+}\)
(b) Fe\(^{2+}\)
(c) Ni\(^{3+}\)
(d) Cu\(^+\)
Show Answer & Explanation

Answer: (b) Fe\(^{2+}\)

Explanation:
1. Zn\(^{2+}\) is \(d^{10}\) (0), Fe\(^{2+}\) is \(d^6\) (4), Ni\(^{3+}\) is \(d^7\) (3), Cu\(^+\) is \(d^{10}\) (0).
2. Only option (b) agrees with this working.

Teacher's Note:
1. For electrons in an atom, check the allowed ranges: l from 0 to n - 1, m from -l to +l and s = +1/2 or -1/2. For ions remove electrons from the outermost shell (4s) before 3d. Magnetic moment = sqrt(n(n+2)) B.M.

Question 11: The configuration of an element is K 2, L 8, M 11, N 2. The number of electrons with l = 2 is
(a) 3
(b) 6
(c) 5
(d) 4
Show Answer & Explanation

Answer: (a) 3

Explanation:
1. The element has 23 electrons (vanadium)
2. M shell \(= 3s^23p^63d^3\), so three electrons have l = 2.

Teacher's Note:
1. For electrons in an atom, check the allowed ranges: l from 0 to n - 1, m from -l to +l and s = +1/2 or -1/2. For ions remove electrons from the outermost shell (4s) before 3d. Magnetic moment = sqrt(n(n+2)) B.M.

Question 12: The orbital angular momentum of an electron in a 2s orbital is
(a) \(\tfrac12\cdot\tfrac{h}{2\pi}\)
(b) \(\dfrac{h}{2\pi}\)
(c) \(\sqrt2\,\dfrac{h}{2\pi}\)
(d) zero
Show Answer & Explanation

Answer: (d) zero

Explanation:
1. For s, l = 0, so \(\sqrt{l(l+1)}\,h/2\pi = 0\).
2. Only option (d) agrees with this working.

Teacher's Note:
1. For electrons in an atom, check the allowed ranges: l from 0 to n - 1, m from -l to +l and s = +1/2 or -1/2. For ions remove electrons from the outermost shell (4s) before 3d. Magnetic moment = sqrt(n(n+2)) B.M.

Question 13: An electron with n = 3 has only one radial node. Its orbital angular momentum is
(a) zero
(b) \(\dfrac{h}{2\pi}\)
(c) \(\sqrt2\,\dfrac{h}{2\pi}\)
(d) \(\sqrt6\,\dfrac{h}{2\pi}\)
Show Answer & Explanation

Answer: (c) \(\sqrt2\,\dfrac{h}{2\pi}\)

Explanation:
1. Radial nodes \(= n-l-1 = 1\) gives l = 1
2. \(L = \sqrt{1\times2}\,h/2\pi = \sqrt2\,h/2\pi\).

Teacher's Note:
1. For electrons in an atom, check the allowed ranges: l from 0 to n - 1, m from -l to +l and s = +1/2 or -1/2. For ions remove electrons from the outermost shell (4s) before 3d. Magnetic moment = sqrt(n(n+2)) B.M.

Question 14: The correct set of four quantum numbers for the valence electron of rubidium (Z = 37) is
(a) n = 5, l = 1, m = 0, s = +1/2
(b) n = 6, l = 0, m = 0, s = +1/2
(c) n = 5, l = 1, m = 1, s = +1/2
(d) n = 5, l = 0, m = 0, s = +1/2
Show Answer & Explanation

Answer: (d) n = 5, l = 0, m = 0, s = +1/2

Explanation:
1. Rb is \([Kr]5s^1\), so n = 5, l = 0, m = 0.
2. Only option (d) agrees with this working.

Teacher's Note:
1. For electrons in an atom, check the allowed ranges: l from 0 to n - 1, m from -l to +l and s = +1/2 or -1/2. For ions remove electrons from the outermost shell (4s) before 3d. Magnetic moment = sqrt(n(n+2)) B.M.

Question 15: The orbital angular momentum values (in units of \(h/2\pi\)) of electrons in 1s, 3s, 3d and 2p orbitals are respectively
(a) 1, 1, 4, 2
(b) 0, 1, \(\sqrt6\), \(\sqrt3\)
(c) 0, 0, \(\sqrt6\), \(\sqrt2\)
(d) 0, 0, \(\sqrt{20}\), \(\sqrt6\)
Show Answer & Explanation

Answer: (c) 0, 0, \(\sqrt6\), \(\sqrt2\)

Explanation:
1. \(L = \sqrt{l(l+1)}\): s gives 0; d (l = 2) gives \(\sqrt6\); p (l = 1) gives \(\sqrt2\).
2. Only option (c) agrees with this working.

Teacher's Note:
1. For electrons in an atom, check the allowed ranges: l from 0 to n - 1, m from -l to +l and s = +1/2 or -1/2. For ions remove electrons from the outermost shell (4s) before 3d. Magnetic moment = sqrt(n(n+2)) B.M.

Question 16: The total number of electrons in the nth shell is given by
(a) \(\sum_{l=1}^{n}2(2l+1)\)
(b) \(\sum_{l=0}^{n-1}2(2l+1)\)
(c) \(\sum_{l=0}^{n}2(2l+1)\)
(d) \(\sum_{l=1}^{n-1}2(2l+1)\)
Show Answer & Explanation

Answer: (b) \(\sum_{l=0}^{n-1}2(2l+1)\)

Explanation:
1. For a given n, l runs from 0 to n - 1 and each subshell holds \(2(2l+1)\) electrons, which sums to \(2n^2\).
2. Only option (b) agrees with this working.

Teacher's Note:
1. For electrons in an atom, check the allowed ranges: l from 0 to n - 1, m from -l to +l and s = +1/2 or -1/2. For ions remove electrons from the outermost shell (4s) before 3d. Magnetic moment = sqrt(n(n+2)) B.M.

Question 17: The spin quantum numbers +1/2 and -1/2 represent
(a) clockwise and anticlockwise rotation
(b) anticlockwise and clockwise rotation
(c) magnetic fields in the same direction
(d) two quantum mechanical spin states which have no classical analogue
Show Answer & Explanation

Answer: (d) two quantum mechanical spin states which have no classical analogue

Explanation:
1. Electron spin has no classical equivalent; clockwise or anticlockwise spinning is only a pictorial aid.
2. Only option (d) agrees with this working.

Teacher's Note:
1. For electrons in an atom, check the allowed ranges: l from 0 to n - 1, m from -l to +l and s = +1/2 or -1/2. For ions remove electrons from the outermost shell (4s) before 3d. Magnetic moment = sqrt(n(n+2)) B.M.

Question 18: Which of the following sets of quantum numbers is impossible for an electron?
(a) n = 4, l = 3, m = -3, s = +1/2
(b) n = 3, l = 0, m = 0, s = -1/2
(c) n = 2, l = 0, m = 1, s = +1/2
(d) n = 5, l = 2, m = 1, s = -1/2
Show Answer & Explanation

Answer: (c) n = 2, l = 0, m = 1, s = +1/2

Explanation:
1. For l = 0, m must be 0, so m = 1 is not allowed.
2. Only option (c) agrees with this working.

Teacher's Note:
1. For electrons in an atom, check the allowed ranges: l from 0 to n - 1, m from -l to +l and s = +1/2 or -1/2. For ions remove electrons from the outermost shell (4s) before 3d. Magnetic moment = sqrt(n(n+2)) B.M.

Question 19: The quantum number n for a given electron describes
(a) shape of the orbital
(b) size and energy of the shell
(c) orientation of the orbital
(d) spin of the electron
Show Answer & Explanation

Answer: (b) size and energy of the shell

Explanation:
1. The principal quantum number fixes the size and the main energy of the orbital
2. The azimuthal quantum number gives the shape.

Teacher's Note:
1. For electrons in an atom, check the allowed ranges: l from 0 to n - 1, m from -l to +l and s = +1/2 or -1/2. For ions remove electrons from the outermost shell (4s) before 3d. Magnetic moment = sqrt(n(n+2)) B.M.

Question 20: Which of the following has the maximum number of unpaired electrons in the ground state?
(a) Ti
(b) V
(c) Mn
(d) Al
Show Answer & Explanation

Answer: (c) Mn

Explanation:
1. Mn \(3d^54s^2\): 5; Ti \(3d^24s^2\): 2; V \(3d^34s^2\): 3; Al \(3p^1\): 1.
2. Only option (c) agrees with this working.

Teacher's Note:
1. For electrons in an atom, check the allowed ranges: l from 0 to n - 1, m from -l to +l and s = +1/2 or -1/2. For ions remove electrons from the outermost shell (4s) before 3d. Magnetic moment = sqrt(n(n+2)) B.M.

Question 21: The ion with the highest spin-only magnetic moment among Fe\(^{3+}\), Cr\(^{3+}\), N\(^{3+}\) and Co\(^{3+}\) is
(a) Cr\(^{3+}\)
(b) Fe\(^{3+}\)
(c) N\(^{3+}\)
(d) Co\(^{3+}\)
Show Answer & Explanation

Answer: (b) Fe\(^{3+}\)

Explanation:
1. Fe\(^{3+}\) (\(d^5\)): 5 unpaired
2. Cr\(^{3+}\) (\(d^3\)): 3
3. N\(^{3+}\) (\(1s^22s^2\)): 0
4. Co\(^{3+}\) (\(d^6\)): 4.

Teacher's Note:
1. For electrons in an atom, check the allowed ranges: l from 0 to n - 1, m from -l to +l and s = +1/2 or -1/2. For ions remove electrons from the outermost shell (4s) before 3d. Magnetic moment = sqrt(n(n+2)) B.M.

Question 22: Of the electrons with quantum numbers (a) n = 4, l = 1; (b) n = 4, l = 0; (c) n = 3, l = 2; (d) n = 3, l = 1, the order of increasing energy is
(a) (d) < (b) < (c) < (a)
(b) (c) < (d) < (b) < (a)
(c) (b) < (d) < (a) < (c)
(d) (a) < (c) < (b) < (d)
Show Answer & Explanation

Answer: (a) (d) < (b) < (c) < (a)

Explanation:
1. By the (n + l) rule: (d) 3p = 4 (n = 3), (b) 4s = 4 (n = 4), (c) 3d = 5 (n = 3), (a) 4p = 5 (n = 4)
2. Equal (n + l): lower n first.

Teacher's Note:
1. For electrons in an atom, check the allowed ranges: l from 0 to n - 1, m from -l to +l and s = +1/2 or -1/2. For ions remove electrons from the outermost shell (4s) before 3d. Magnetic moment = sqrt(n(n+2)) B.M.

Question 23: The set of quantum numbers n = 2, l = 2, m = 0 for an electron
(a) refers to a 2d electron
(b) denotes a 2p electron
(c) is not allowed
(d) describes one of the 7f orbitals
Show Answer & Explanation

Answer: (c) is not allowed

Explanation:
1. For n = 2, l can only be 0 or 1, so l = 2 is impossible.
2. Only option (c) agrees with this working.

Teacher's Note:
1. For electrons in an atom, check the allowed ranges: l from 0 to n - 1, m from -l to +l and s = +1/2 or -1/2. For ions remove electrons from the outermost shell (4s) before 3d. Magnetic moment = sqrt(n(n+2)) B.M.

Structure Of Atom Objective Questions & Solutions for JEE Chemistry

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