Give reasons for the following

A crusty 'boiler scale' is formed in boilers, when hard water is used.

Name or state the following.

1. An efflorescent decahydrate salt.
2. A deliquescent salt of a trivalent metal.
3. A liquid hygroscopic substance.
4. A salt whose solubility decreases with rise in temperature of the solvent water.
5. A substance added to remove both temporary and permanent hardness in water.

Differentiate between the following :

Saturated solution and super saturated solution

Differentiate between the following :

Solubility and solubility curve