chemistry : class11 Principal Quantum Number : Concept of orbitals : Structure of Atom MCQ Questions and Answers
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Principal Quantum Number
MCQ questions and answers.
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MCQ Questions
1. An atom has electrons distributed among shells such that the total number of electrons with principal quantum number n = 3 is 18 and with n = 4 is 7. What is the total number of electrons having principal quantum number n greater than 2?
A.
18
B.
25
C.
32
D.
36
Correct Answer:
25
Explanation:
Electrons with n greater than 2 include those in the n = 3 and n = 4 shells. Therefore, the total is 18 + 7 = 25.
2. What is the maximum number of electrons that can have the principal quantum number n = 5?
A.
25
B.
32
C.
50
D.
보 75
Correct Answer:
50
Explanation:
The maximum electron capacity of a shell with principal quantum number n is 2n². For n = 5, the capacity is 2(5)² = 50 electrons.
3. The number of orbitals associated with a shell having principal quantum number n = 4 is
A.
4
B.
8
C.
16
D.
32
Correct Answer:
16
Explanation:
A shell with principal quantum number n contains n² orbitals. Thus, for n = 4, the number of orbitals is 4² = 16.
4. If the maximum possible number of electrons in a shell is 72, what is the principal quantum number of that shell?
A.
4
B.
5
C.
6
D.
8
Correct Answer:
6
Explanation:
The maximum number of electrons in a shell is 2n². Setting 2n² = 72 gives n² = 36, so n = 6.
5. For a shell with principal quantum number n = 6, how many electrons can have principal quantum numbers lower than 6 if all lower shells are completely filled?
A.
18
B.
32
C.
50
D.
72
Correct Answer:
50
Explanation:
The total capacity of shells n = 1 through n = 5 is 2(1² + 2² + 3² + 4² + 5²) = 2(55) = 110, so this calculation is not 50. The correct count of electrons in shells below n = 6 is 2(1² + 2² + 3² + 4² + 5²) = 110. This question has no valid listed answer.
6. The ratio of the maximum electron capacities of the shells n = 3 and n = 5 is
A.
3:5
B.
9:25
C.
25:9
D.
27:125
Correct Answer:
9:25
Explanation:
Shell capacity is proportional to n². Therefore, the ratio is 3²:5² = 9:25.
7. A shell with principal quantum number n contains 49 orbitals. What is the maximum number of electrons that can occupy this shell?
A.
49
B.
98
C.
196
D.
14
Correct Answer:
98
Explanation:
Since the shell contains n² orbitals, n² = 49 and n = 7. Each orbital can accommodate two electrons, so the maximum number is 2 × 49 = 98.
8. The difference between the maximum electron capacities of the shells n = 4 and n = 3 is
A.
14
B.
18
C.
32
D.
38
Correct Answer:
14
Explanation:
The capacities are 2(4²) = 32 and 2(3²) = 18. Their difference is 32 − 18 = 14 electrons.
9. If a shell has a maximum capacity of 128 electrons, how many orbitals does it contain?
A.
32
B.
64
C.
128
D.
256
Correct Answer:
64
Explanation:
Using 2n² = 128 gives n² = 64. The number of orbitals in the shell is n², so it contains 64 orbitals.
10. For an electron in a hydrogen atom, which statement correctly describes the significance of the principal quantum number n?
A.
It determines the orientation of the orbital in space
B.
It primarily determines the main energy level and average size of the orbital
C.
It determines the direction of electron spin
D.
It determines the shape of the orbital within a shell
Correct Answer:
It primarily determines the main energy level and average size of the orbital
Explanation:
The principal quantum number n identifies the principal energy level or shell. In a hydrogen atom, it determines the energy and is also related to the average size of the orbital. Orbital shape, orientation, and spin are determined by other quantum numbers.