Answer:
200 cm
Step-by-step explanation:
To find the wavelength of the least sound produced by the air column, you take into account that for the first mode you have that the wavelength is four times the length of the column:
![\lambda=4L](https://img.qammunity.org/2021/formulas/physics/high-school/5ox2wb2bnn6erx3arbvywl5tt1s5otczrr.png)
This is because the sound is reflected in the column in such a way that only one quarter of the wavelength of the sound, allows one to obtain a mode of resonance into the air column.
Furthermore, this correspond to the least frequency because in this system the frequency is given by:
![f_n=(nv_s)/(4L)=(v_s)/(\lambda_n)\\\\\lambda=4L](https://img.qammunity.org/2021/formulas/physics/high-school/36c7z9ey7f9f14qhh1x9asqfu4yfx9g9xp.png)
It is clear that for n=1 you obtain the least frequency.
By replacing the value of L you obtain:
![\lambda=4(50cm)=200cm](https://img.qammunity.org/2021/formulas/physics/high-school/sp3q0pca51v1objeejy983jip5vyr6nw2b.png)
hence, the wavelength is 200 cm