JEE Chemistry Atomic Structure MCQs Set 03

Download JEE MCQs for JEE Chemistry: Atomic Structure

Explore reliable objective questions for Atomic Structure tailored for JEE learners. Utilizing these Chemistry multiple-choice formats ensures thorough preparation and strengthens problem-solving speed for upcoming school assessments.

Chapter-wise Objective Questions: Atomic Structure

Access the complete set of multiple-choice questions for Atomic Structure below. This focused format allows students to isolate specific topics for thorough review and uninterrupted practice alongside official JEE textbooks.

Multiple Choice Questions

Question 1: If the de Broglie wavelength of the fourth Bohr orbit of the hydrogen atom is 4 Å, the circumference of the orbit will be:
(a) 4 Å
(b) 4 nm
(c) 16 Å
(d) 16 nm
Show Answer & Explanation

Answer: (c) 16 Å

Explanation:
1. Circumference 2πr = nλ = 4 × 4 Å = 16 Å.
2. Answer: (c)

Teacher's Note:
1. Use the Bohr formulas for hydrogen-like species.
2. Check units and the value of Z.

Question 2: What is the ratio of the de Broglie wavelengths for electrons accelerated through 200 volts and 50 volts?
(a) 1 : 2
(b) 2 : 1
(c) 3 : 10
(d) 10 : 3
Show Answer & Explanation

Answer: (a) 1 : 2

Explanation:
1. λ ∝ 1/√V.
2. λ200/λ50 = √(50/200) = 1/2.
3. Answer: (a)

Teacher's Note:
1. Use the Bohr formulas for hydrogen-like species.
2. Check units and the value of Z.

Question 3: The uncertainty in the position of an electron and a helium atom is the same. If the uncertainty in the momentum of the electron is 32 × 105, the uncertainty in the momentum of the helium atom will be:
(a) 32 × 105
(b) 16 × 105
(c) 8 × 105
(d) None of these
Show Answer & Explanation

Answer: (a) 32 × 105

Explanation:
1. Δx·Δp ≥ h/4π, so with the same Δx the minimum Δp is the same.
2. Δp (He) = 32 × 105.
3. Answer: (a)

Teacher's Note:
1. Use the Bohr formulas for hydrogen-like species.
2. Check units and the value of Z.

Question 4: The quantum numbers n = 3, l = 2 and m = +2 are possible for how many orbitals?
(a) 1
(b) 2
(c) 3
(d) 4
Show Answer & Explanation

Answer: (a) 1

Explanation:
1. n, l and m together define one orbital, so just 1.
2. Answer: (a)

Teacher's Note:
1. Use the Bohr formulas for hydrogen-like species.
2. Check units and the value of Z.

Question 5: A nodal plane is found in which orbital?
(a) n = 2, l = 0
(b) n = 3, l = 0
(c) n = 2, l = 1
(d) n = 1, l = 0
Show Answer & Explanation

Answer: (c) n = 2, l = 1

Explanation:
1. s orbitals are spherical and have no nodal plane; a p orbital (n = 2, l = 1) has one nodal plane.
2. Answer: (c)

Teacher's Note:
1. Use the Bohr formulas for hydrogen-like species.
2. Check units and the value of Z.

Question 6: The number of orbitals in an h sub-shell is:
(a) 11
(b) 15
(c) 17
(d) 19
Show Answer & Explanation

Answer: (a) 11

Explanation:
1. h has l = 5, so 2l + 1 = 11 orbitals.
2. Answer: (a)

Teacher's Note:
1. Use the Bohr formulas for hydrogen-like species.
2. Check units and the value of Z.

Question 7: Which of the following is correct for a 4d electron?
(a) n = 4, l = 2, s = +1/2
(b) n = 4, l = 2, s = 0
(c) n = 4, l = 3, s = 0
(d) n = 4, l = 3, s = +1/2
Show Answer & Explanation

Answer: (a) n = 4, l = 2, s = +1/2

Explanation:
1. 4d means n = 4 and l = 2; spin is ±1/2 (never 0).
2. Answer: (a)

Teacher's Note:
1. Use the Bohr formulas for hydrogen-like species.
2. Check units and the value of Z.

Question 8: The spin angular momentum of an electron is:
(a) √(s(s + 1)) h/2π
(b) √(2s(s + 1)) h/2π
(c) √(s(s + 2)) h/2π
(d) None of these
Show Answer & Explanation

Answer: (a) √(s(s + 1)) h/2π

Explanation:
1. Spin angular momentum = √(s(s + 1)) × h/2π with s = 1/2.
2. Answer: (a)

Teacher's Note:
1. Use the Bohr formulas for hydrogen-like species.
2. Check units and the value of Z.

Question 9: The total number of orbitals (counting every different value of m in every sub-shell) in the n = 4 shell is:
(a) 4
(b) 8
(c) 16
(d) 32
Show Answer & Explanation

Answer: (c) 16

Explanation:
1. The number of orbitals in a shell is n2 = 16 (1 + 3 + 5 + 7).
2. Answer: (c)

Teacher's Note:
1. Use the Bohr formulas for hydrogen-like species.
2. Check units and the value of Z.

Question 10: In an atom, for how many electrons can the quantum numbers be n = 3, l = 2, m = +2, s = +1/2?
(a) 18
(b) 6
(c) 24
(d) 1
Show Answer & Explanation

Answer: (d) 1

Explanation:
1. The four quantum numbers fully specify a single electron, so only 1.
2. Answer: (d)

Teacher's Note:
1. Use the Bohr formulas for hydrogen-like species.
2. Check units and the value of Z.

Question 11: A neutral atom of an element has 2K, 8L, 11M and 2N electrons. The number of s-electrons in the atom is:
(a) 2
(b) 8
(c) 10
(d) 6
Show Answer & Explanation

Answer: (b) 8

Explanation:
1. The s sub-shells filled are 1s, 2s, 3s and 4s, each with 2 electrons.
2. Total = 8.
3. Answer: (b)

Teacher's Note:
1. Use the Bohr formulas for hydrogen-like species.
2. Check units and the value of Z.

Question 12: If l = 3, then the type and number of orbitals is:
(a) 3p, 3
(b) 4f, 14
(c) 5f, 7
(d) 3d, 5
Show Answer & Explanation

Answer: (c) 5f, 7

Explanation:
1. l = 3 is an f sub-shell, and it has 2l + 1 = 7 orbitals.
2. The only option with f and 7 is 5f, 7.
3. Answer: (c)

Teacher's Note:
1. Use the Bohr formulas for hydrogen-like species.
2. Check units and the value of Z.

Question 13: The orbital with maximum energy is:
(a) 3d
(b) 5p
(c) 4s
(d) 6d
Show Answer & Explanation

Answer: (d) 6d

Explanation:
1. Compare n + l: 3d = 5, 5p = 6, 4s = 4, 6d = 8.
2. 6d has the largest n + l, so it has the maximum energy.
3. Answer: (d)

Teacher's Note:
1. Use the Bohr formulas for hydrogen-like species.
2. Check units and the value of Z.

Question 14: The n and l values of an orbital A are 3 and 2, and of another orbital B are 5 and 0. The energy of:
(a) B is more than A
(b) A is more than B
(c) A and B are of the same energy
(d) None of these
Show Answer & Explanation

Answer: (a) B is more than A

Explanation:
1. n + l = 5 for both; with equal n + l, the orbital with the larger n has the higher energy.
2. So E(B) > E(A).
3. Answer: (a)

Teacher's Note:
1. Use the Bohr formulas for hydrogen-like species.
2. Check units and the value of Z.

Question 15: The number of all subshells with n + l = 7 is:
(a) 4
(b) 5
(c) 6
(d) 7
Show Answer & Explanation

Answer: (a) 4

Explanation:
1. Allowed pairs (n, l): (7, 0), (6, 1), (5, 2), (4, 3).
2. So 4 sub-shells.
3. Answer: (a)

Teacher's Note:
1. Use the Bohr formulas for hydrogen-like species.
2. Check units and the value of Z.

Question 16: For Na (Z = 11), the set of quantum numbers for the last electron is:
(a) n = 3, l = 1, m = 1, s = +1/2
(b) n = 3, l = 0, m = 0, s = +1/2
(c) n = 3, l = 0, m = 1, s = +1/2
(d) n = 3, l = 1, m = 1, s = −1/2
Show Answer & Explanation

Answer: (b) n = 3, l = 0, m = 0, s = +1/2

Explanation:
1. Na = 1s2 2s2 2p6 3s1.
2. The last electron is in 3s: n = 3, l = 0, m = 0, s = +1/2.
3. Answer: (b)

Teacher's Note:
1. Use the Bohr formulas for hydrogen-like species.
2. Check units and the value of Z.

Question 17: The atomic number of an element is 17. The number of orbitals containing electron pairs in the valence shell is:
(a) 8
(b) 2
(c) 3
(d) 6
Show Answer & Explanation

Answer: (c) 3

Explanation:
1. Cl: 3s2 3p5; the 3s orbital is a pair and two of the three 3p orbitals hold pairs.
2. Total = 3.
3. Answer: (c)

Teacher's Note:
1. Use the Bohr formulas for hydrogen-like species.
2. Check units and the value of Z.

Question 18: What is the electronic configuration, in its first excited state, of an element isoelectronic with O2 (that is, of 16 electrons)?
(a) [Ne] 3s2 3p3 3d1
(b) [Ne] 3s2 3p4
(c) [Ne] 3s1 3p3 3d2
(d) [Ne] 3s1 3p5
Show Answer & Explanation

Answer: (a) [Ne] 3s2 3p3 3d1

Explanation:
1. O2 has 16 electrons, like sulfur: [Ne] 3s2 3p4 in the ground state.
2. Promoting one 3p electron to 3d gives the first excited state [Ne] 3s2 3p3 3d1.
3. Answer: (a)

Teacher's Note:
1. Use the Bohr formulas for hydrogen-like species.
2. Check units and the value of Z.

Question 19: The number of electrons in the M-shell of the element with atomic number 24 is:
(a) 24
(b) 12
(c) 8
(d) 13
Show Answer & Explanation

Answer: (d) 13

Explanation:
1. Cr (Z = 24): 1s2 2s2 2p6 3s2 3p6 3d5 4s1.
2. M-shell (n = 3) = 2 + 6 + 5 = 13.
3. Answer: (d)

Teacher's Note:
1. Use the Bohr formulas for hydrogen-like species.
2. Check units and the value of Z.

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