Which of these solution have the lowest vapor pressure in 298 K?
All examples are mixtures of not-volatile (here: salts, but it would be the same for a teaspoon of sugar) and volatile compounds.

The vapour pressure above these mixtures is proportional to the mole fraction of the volatile component. With other words:

The higher the concentation of the salt, the lower the vapour pressure.

But as user80551 pointed out in his comment, we should not look at it this way. Water isn't "just the solvent" here.

It is the volatile compound in the mixture that matters! The higher the mole fraction of the volatile compound, the higher the vapour pressure!

With (again) other words: Raoult's Law ;)