Rank the following substances in order of increasing vapor pressure at a fixed temperature: H_2O, CH_3Cl, He, NaCl.

a) He < NaCl < H2O < CH3Cl
b) NaCl < He < CH3Cl < H2O
c) NaCl < He < H2O < CH3Cl
d) He < H2O < NaCl < CH3Cl