A pipe of length $85\;cm$ is closed from one end. Find the number of possible natural oscillations of air column in the pipe whose frequencies lie below $1250\; Hz$. The velocity of sound in air is $340\; m/s$.

Question

$\begin{array}{1 1}(A)\;6 \\ (B)\;4 \\(C)\;12 \\(D)\;8 \end{array} $