When a ray of light passes through a thin walled hollow glass prism of thickness t and refractive index 1.5.which one is wrong?

maximum deviation takes places

When a ray of light passes through a glass slab of uniform thickness the incident ray is parallel to the imergent ray. Therefore no angular deviation takes place. We know that the ray of light when passing through a thin walled glass suffers a lateral shift $x = t(1-\frac{1}{μ})=t(1-\frac{1}{1.5})=\frac{t}{3}$
in first wall 1. Similarly in second wall 2 it suffers a lateral shift of equal magnitude. Therefore the total lateral shift is equal to $\frac{2t}{3}$. In each case there will be no angular deviation. Therefore no dispersion takes place.