Name two processes which remove carbon dioxide from the atmosphere.

Explain the following :

A white crust forms on the surface of lime water that has been exposed to the atmosphere.

State your observations and give balanced equations of the reactions when carbon dioxide is passed through clear lime water (a) for a short time (b) for a long time.

XCl₂ is the chloride of a metal X. State the formula of the sulphate and the hydroxide of the metal X.