An open organ pipe produces a fundamental frequency of 300 Hz . If...

The fundamental frequency of an open organ pipe of length $L$ is given by $f_{\text{open}} = \dfrac{v}{2L}$.

Given $f_{\text{open}} = 300\text{ Hz}$.

When one end of the pipe is tightly closed, it behaves as a closed organ pipe. The fundamental frequency of a closed organ pipe of the same length $L$ is given by $f_{\text{closed}} = \dfrac{v}{4L}$.

Comparing the two frequencies, we get $f_{\text{closed}} = \dfrac{1}{2} \left(\dfrac{v}{2L}\right) = \dfrac{f_{\text{open}}}{2}$.

Substituting the given value, $f_{\text{closed}} = \dfrac{300}{2} = 150\text{ Hz}$.

Answer: $150\text{ Hz}$