If sound travels in air with the speed of 340ms^ - 1 , then the...

Given, speed of sound, $v = 340ms^{- 1}$
Length of open organ pipe, $l = 2m$

Frequency, $f = 1200Hz$
For open organ pipe,

Fundamental frequency, ${f}_{0} = \dfrac{v}{2l} = \dfrac{340}{2 \times 2} = 85$

$∴$ Number of tones present in the open organ pipe
$= \dfrac{f}{f0} = \dfrac{1200}{85} = 14. 11 ≃ 14$