The most basic solution out of water, lemon juice, ammonia, and cola is ammonia. Here's why:

* Acids: Lemon juice and cola are acidic. They have a pH less than 7.

* Neutral: Water is neutral, with a pH of 7.

* Base: Ammonia is a base, with a pH greater than 7.

pH scale: The pH scale measures the acidity or alkalinity of a solution.

* 0-6: Acidic

* 7: Neutral

* 8-14: Basic (alkaline)

Therefore, ammonia is the most basic solution out of the options given.