Step 1: Understanding the Question:
A closed pipe (closed at one end, open at the other) in its fundamental mode. The time for sound to travel from the open end to the closed end is \(t\). We need the frequency.
Step 2: Key Formula or Approach:
For a closed pipe, fundamental frequency \(f = \frac{v}{4L}\), where \(L\) is the length of the pipe. The time to travel from open end to closed end is \(t = \frac{L}{v}\) (distance \(L\), speed \(v\)). Thus \(v = L/t\).
Step 3: Detailed Explanation:
Substitute \(v = L/t\) into \(f = \frac{v}{4L}\):
\[
f = \frac{L/t}{4L} = \frac{1}{4t} = \frac{0.25}{t}.
\]
Step 4: Final Answer:
Frequency = \(\frac{0.25}{t}\), option (D).