Since Px = (2/l) sin2(np x/l), with n = 3, the peak value labelled "x" is equal to 2/l: i.e.where the sin = 1. These points are at (1/6)l, (3/6)l = (1/2)l and (5/6)l

The area under the curve = total probability of finding the electron somewhere on the molecule = 1.

For n = 3 the wave function has 3 loops.

Answer is D