The molecule having smallest bond angle is: AsCl3, PCl3, SbCl3, NCl3

As electronegativity of central atom decreases, bond angle decreases. Sb is the least electronegative and hence, it has the smallest bond angle. The correct order of bond angle: NCl3 > PCl3 > AsCl3 > SbCl3. Hence, option SbCl3 is correct.