Answer
The correct answer is:
(b) 5
Work Step by Step
A pipe that is closed at one end can only produce odd harmonics. That is, the pipe can produce $f_1, ~3f_1, ~5f_1, ~7f_1,~9f_1,~etc...$
The frequency $f_1$ has one node. For each successive frequency produced, there is one additional node. Since $9f_1$ is the fifth highest frequency produced, there are five nodes.
The correct answer is:
(b) 5
