Water of Crystallisation

A hydrate of ${\mathrm{Na}}_2{\mathrm{SO}}_3$ has $50 \%$ of water by mass. It is:

A solution of aluminium sulphate in water is _____.

When crystals of copper sulphate are strongly heated the residue obtained is 

Identify the efflorescent substance from the following:

Efflorescence is a process in which crystalline salt loses its shape and turns powdery. What is true in this context:

When crystals of copper sulphate are strongly heated, the residue obtained is

${\mathrm{Na}}_2{\mathrm{SO}}_4·10{\mathrm{H}}_2\mathrm{O}$ is an example of:

Why does the blue colour of copper sulphate pentahydrate changes on heating? 

What is water of crystallisation? What is the difference between hydrated and anhydrous salt? What is the effect of heating on hydrated salts? 

${\mathrm{Al}}_2{\mathrm{CO}}_3.2{\mathrm{H}}_2\mathrm{O}$ and ${\mathrm{Na}}_2{\mathrm{CO}}_3.10{\mathrm{H}}_2\mathrm{O}$ are two anhydrous salts. 

Anhydrous substances contain water of crystallisation.