A pipe open at both ends has a fundamental frequency f in air. The pipe is dipped vertically in water so that half of it is in water. The fundamental frequency of the air column is now :

Question

$\begin{array}{1 1} (1) \large\frac{f}{2} \\ (2) \large\frac{3f}{4} \\ (3) 2f \\ (4) f \end{array} $