An open organ pipe has a fundamental frequency of 300text{ Hz}. If one end of the pipe is now closed, the new fundamental frequency will be:

The fundamental frequency of an open organ pipe of length $L$ is $f_{\text{open}} = \frac{v}{2L} = 300\text{ Hz}$. When one end is closed, the length remains the same, and the new fundamental frequency becomes $f_{\text{closed}} = \frac{v}{4L}$. Comparing the two, $f_{\text{closed}} = \frac{1}{2} f_{\text{open}} = \frac{300}{2} = 150\text{ Hz}$.