Question:

An air column, closed at one end and open at the other, resonates with a tuning fork when the smallest length of the column is 50 cm. The next larger length of the column resonating with the same tuning fork is:

200 cm

66.7 cm

150 cm

100 cm

First minimum resonating length of column for closed organ pipe is λ/4 = 50 cm
Next larger length of column for resonating will be 3λ/4 = 150 cm