What is 'X' in the given reaction?

Water does not produce CO on reacting with :

The solubility of Ca(OH)₂ in water is :

[Given : The solubility product of Ca(OH)₂ in water = 5.5 $$\times$$ 10^$$-$$6]

Given below are two statements :

Statement I : The pH of rain water is normally 5.6.

Statement II : If the pH of rain water drops below 5.6, it is called acid rain.

In the light of the above statements, choose the correct answer from the options given below :