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 gives the most precise definition of an atomic orbital?
A.
A fixed circular path followed by an electron around the nucleus
B.
A three-dimensional region around the nucleus where the probability of finding an electron is high
C.
The complete set of allowed energy levels in an atom
D.
The distance between the nucleus and the outermost electron
Correct Answer:
A three-dimensional region around the nucleus where the probability of finding an electron is high
Explanation:
An orbital is a three-dimensional region of space described by a wave function in which there is a high probability of finding an electron. It is not a definite path or orbit.
2. Why is an orbital not correctly described as the path of an electron around the nucleus?
A.
Because electrons have no kinetic energy
B.
Because an orbital represents a probability distribution rather than a definite trajectory
C.
Because the nucleus occupies the entire orbital
D.
Because electrons can exist only outside the atom
Correct Answer:
Because an orbital represents a probability distribution rather than a definite trajectory
Explanation:
The orbital concept is based on the wave-mechanical description of the electron. It specifies the probability distribution of the electron, not a precisely traceable path.
3. An orbital boundary is commonly drawn to enclose approximately 90% of the electron probability. What does the remaining probability imply?
A.
The electron is destroyed outside the boundary
B.
The electron must be moving in a circular orbit outside the boundary
C.
There is still a small probability of finding the electron outside the drawn boundary
D.
The orbital has a second nucleus outside the boundary
Correct Answer:
There is still a small probability of finding the electron outside the drawn boundary
Explanation:
An orbital boundary is a chosen probability surface, not a rigid physical wall. The electron may still be found outside it, although with lower probability.
4. Which statement correctly distinguishes an orbital from a shell?
A.
An orbital is a probability region, whereas a shell is a principal energy level containing one or more subshells
B.
An orbital contains several shells, whereas a shell contains one electron
C.
An orbital is a circular path, whereas a shell is a wave function
D.
An orbital and a shell are identical terms for the same region of space
Correct Answer:
An orbital is a probability region, whereas a shell is a principal energy level containing one or more subshells
Explanation:
An orbital is a specific region described by an electron wave function. A shell is a broader energy classification that may contain several subshells and orbitals.
5. Which feature is essential to the definition of an orbital in quantum mechanics?
A.
It must have a circular shape
B.
It must contain exactly two electrons
C.
It is described by a wave function that determines the electron probability distribution
D.
It must be located at a fixed distance from the nucleus
Correct Answer:
It is described by a wave function that determines the electron probability distribution
Explanation:
An orbital is mathematically represented by a wave function. The square of the wave function is related to the probability density of finding the electron at a particular location.
6. A diagram displays a dumbbell-shaped region around a nucleus. What does this diagram primarily represent?
A.
The exact route taken by an electron
B.
A region of space associated with a high probability of finding an electron
C.
The physical surface of the nucleus
D.
The boundary of the atom containing all possible electron positions with certainty
Correct Answer:
A region of space associated with a high probability of finding an electron
Explanation:
Orbital diagrams show the spatial probability distribution of an electron. The displayed shape is not an electron trajectory or a rigid surface.
7. If two electrons occupy the same orbital, which conclusion follows directly from the meaning of orbital?
A.
They necessarily follow identical paths around the nucleus
B.
They are associated with the same spatial probability distribution
C.
They must be at the same position at every instant
D.
They must have different principal energy levels
Correct Answer:
They are associated with the same spatial probability distribution
Explanation:
Electrons in the same orbital share the same orbital wave function and therefore the same spatial probability distribution. An orbital does not specify an individual electron path.
8. Which statement about the location of an electron in an orbital is scientifically accurate?
A.
Its exact position is permanently fixed within the orbital
B.
Its position can be assigned only to the nucleus or the orbital boundary
C.
Its location is described probabilistically throughout the orbital region
D.
It is always found at the point of maximum probability
Correct Answer:
Its location is described probabilistically throughout the orbital region
Explanation:
An orbital gives the probability of finding an electron at different points in space. Even within an orbital, the electron is not restricted to one fixed location.
9. Which statement would make an electron distribution unsuitable for being called a single orbital?
A.
It is represented by a normalized wave function
B.
It describes a probability distribution in three-dimensional space
C.
It represents a definite classical trajectory traced by the electron
D.
It has a characteristic spatial pattern determined by the wave function
Correct Answer:
It represents a definite classical trajectory traced by the electron
Explanation:
An orbital is a quantum-mechanical probability distribution, not a classical path. A definite trajectory therefore contradicts the orbital definition.
10. Why can an orbital be represented by a boundary surface even though the electron is not confined by that surface?
A.
The boundary is chosen to enclose a specified high probability of finding the electron
B.
The boundary is the exact outer surface of the electron
C.
The boundary marks the point where electron probability becomes permanently zero in every case
D.
The boundary is formed by the electron's circular motion
Correct Answer:
The boundary is chosen to enclose a specified high probability of finding the electron
Explanation:
Orbital boundary surfaces are visual tools used to show regions containing a selected percentage of electron probability. They do not physically confine the electron or necessarily make probability zero outside.