How do you test the nature of the solution formed by dissolving `CaO` in water? what is the nature of the solution?

The nature of CaO is

How do you test the CO_2 gas ?

What is the nature of aqueous borax solution ?

What is the nature of aqueous borax solution ?

How do you think they are formed there?

How do you test the pH of the soil in the agriculture field ?

Calculate the molarity of NaOH in the solution prepared by dissolving its 4 g in enough water to form 250 mL of the solution.

Calculate the molarity of a solution prepared by dissolving its 4g NaOH in enough water to form 250mL of the solution.