How to arrange substances in order of increasing vapor pressure?
To solve this problem, use Raoult's law. In Raoult's law, the vapor pressure of a fluid is lowered proportionally with the mole fraction of solute particles in the fluid.
You know the formula, but you only need it if you want to calculate the actual resulting vapor pressure. We can know which is bigger like this:
A. $\pu{0.5M }$ sugar. Sugar does not ionize, thus there are $\pu{0.5 M }$ particles in the solvent.
B. $\pu{0.5M \ce{NaCl}}$. Sodium chloride dissociates to two ions. Thus there are $0.5 \times \pu{2 M}$ particles in the solvent.
C. $\pu{2M}$ ethylene glycol. Again, this doesn't dissociate, so there are $\pu{2M}$ particles.
D. $\pu{2M \ce{LiBr}}$. Dissociates, resulting in $2 \times \pu{2 M}$ particles.
Thus, listing the concentration of particles in the solvent, you see where the answer comes from:
D: $\pu{4 M}$
C: $\pu{2 M}$
B: $\pu{1 M}$
A: $\pu{0.5 M}$