The Correct answer is "d) Eighth note".

Explanation:
- The duration of a musical note refers to how long the note is held or played.
- In music notation, the duration of a note is represented by the shape of the note and the presence of flags or beams attached to it.
- The shorter the duration of a note, the faster it is played or held.
- Let's examine the durations of the notes mentioned in the options:

a) Quarter note:
- A quarter note is represented by a solid oval shape with a straight stem.
- It has a duration of one beat in common time or 4/4 time signature.
- It is played or held for a moderate duration.

b) Half note:
- A half note is represented by a solid oval shape with a straight stem and a hollow center.
- It has a duration of two beats in common time or 4/4 time signature.
- It is played or held for a longer duration than a quarter note.

c) Whole note:
- A whole note is represented by a solid oval shape without a stem.
- It has a duration of four beats in common time or 4/4 time signature.
- It is played or held for a longer duration than a half note.

d) Eighth note:
- An eighth note is represented by a solid oval shape with a straight stem and a flag attached to it.
- It has a duration of half a beat in common time or 4/4 time signature.
- It is played or held for a very short duration, making it the shortest note among the options given.

Conclusion:
- Among the given options, the eighth note has the shortest duration.
- It is played or held for half a beat, making it the shortest note in terms of duration.