chemistry : class11 Orbital Definition : Concept of orbitals : Structure of Atom MCQ Questions and Answers
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Orbital Definition
MCQ questions and answers.
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MCQ Questions
1. Which statement most precisely defines an atomic orbital?
A.
A definite circular path followed by an electron around the nucleus
B.
A region of space around the nucleus where the probability of finding an electron is high
C.
A fixed energy shell containing all electrons with the same principal quantum number
D.
A straight-line trajectory along which an electron moves with constant speed
Correct Answer:
A region of space around the nucleus where the probability of finding an electron is high
Explanation:
An atomic orbital is a three-dimensional region in which the probability of finding an electron is high. It is not a definite path or trajectory.
2. The boundary surface commonly drawn for an orbital represents a surface within which the probability of finding the electron is approximately:
A.
Exactly 0%
B.
Exactly 50% for every orbital
C.
A large selected percentage, usually about 90–95%
D.
100% under all conditions
Correct Answer:
A large selected percentage, usually about 90–95%
Explanation:
An orbital boundary is conventionally drawn to enclose a high, selected probability of finding the electron. It is not a rigid physical wall and does not imply certain presence.
3. Which observation most directly distinguishes an orbital from a classical orbit?
A.
An orbital has a definite radius at every instant
B.
An orbital specifies a probability distribution rather than an electron trajectory
C.
An orbital can contain an unlimited number of electrons
D.
An orbital exists only when an electron is moving in a circular path
Correct Answer:
An orbital specifies a probability distribution rather than an electron trajectory
Explanation:
An orbital describes the probability distribution associated with an electron through its wavefunction; it does not specify a classical path.
4. If the probability density at a point in an orbital is zero, what does this imply?
A.
The electron must remain permanently outside the orbital
B.
The electron cannot be found at that point in that orbital
C.
The orbital has zero total energy
D.
The nucleus is absent from the orbital
Correct Answer:
The electron cannot be found at that point in that orbital
Explanation:
Zero probability density at a point means that an electron described by that orbital has zero probability of being detected at that location.
5. Why is the phrase “the electron revolves in an orbital” scientifically inappropriate?
A.
Orbitals contain no energy information
B.
An orbital is a probability distribution and does not define a mechanical path
C.
Electrons are stationary particles with no wave nature
D.
An orbital is located only inside the nucleus
Correct Answer:
An orbital is a probability distribution and does not define a mechanical path
Explanation:
The term orbital refers to a wave-mechanical region of probable electron location, not to a path around the nucleus.
6. Which statement about the shape of an orbital is most accurate?
A.
It is the exact route traced by an electron
B.
It is determined by the spatial distribution of electron probability
C.
It is always spherical because every electron has the same motion
D.
It is determined only by the electron's instantaneous speed
Correct Answer:
It is determined by the spatial distribution of electron probability
Explanation:
Orbital shapes, such as spherical or dumbbell-shaped distributions, represent how electron probability is distributed in space.
7. An orbital boundary is changed from a 90% probability surface to a 99% probability surface. What happens to the orbital itself?
A.
The orbital changes into a different subshell
B.
The electron gains an additional quantum number
C.
The drawn boundary becomes larger, but the orbital state remains the same
D.
The orbital ceases to exist because its probability is no longer fixed
Correct Answer:
The drawn boundary becomes larger, but the orbital state remains the same
Explanation:
Orbital boundaries are visual conventions based on a chosen probability percentage. Changing the percentage changes the displayed boundary, not the underlying orbital.
8. Which quantity is directly associated with the physical interpretation of an orbital wavefunction?
A.
The square of the wavefunction gives probability density
B.
The wavefunction itself gives the exact electron path
C.
The reciprocal of the wavefunction gives electron mass
D.
The wavefunction gives the electron's fixed position at all times
Correct Answer:
The square of the wavefunction gives probability density
Explanation:
For an orbital wavefunction, the square of its magnitude, written as |ψ|², gives the probability density of finding the electron at a location.
9. Which statement correctly describes the relationship between an orbital and electron location?
A.
An orbital predicts one exact position for the electron
B.
An orbital identifies a region where electron detection is more probable
C.
An orbital guarantees that the electron is present at every point inside it
D.
An orbital places the electron only on its outer boundary
Correct Answer:
An orbital identifies a region where electron detection is more probable
Explanation:
An orbital provides a spatial probability distribution, indicating regions where detecting the electron is more or less likely.
10. Two diagrams of the same orbital use boundary surfaces enclosing 85% and 95% probability, respectively. Which conclusion is valid?
A.
They necessarily represent two different orbitals
B.
The 95% diagram represents a different electron shell
C.
They can represent the same orbital drawn using different probability cutoffs
D.
The 85% diagram cannot represent a valid orbital
Correct Answer:
They can represent the same orbital drawn using different probability cutoffs
Explanation:
An orbital is not uniquely defined by one arbitrary boundary percentage. Different cutoff values can produce different-sized depictions of the same probability distribution.