Answer
a. Stirring the solution.
Explanation
When preparing a saturated solution of sodium nitrate in water, the following actions would speed up the rate of solution.
i. Temperature, basically, solubility increases with temperature.
ii. Polarity. In most cases, solutes dissolve in solvents that have a similar polarity.
iii. Pressure.
iv. Molecular size (surface area).
v. Stirring increases the speed of dissolving.
Therefore, the correct answer is option a. Stirring the solution.
