Dispersion and Impure Spectrum:

Dispersion : The phenomenon due to which a polychromatic light splits into component colours, when passed through a prism is called 'dispersion'.

Impure Spectrum : A Spectrum in which various bands of colours have no sharp well defined  boundaries, but merge in each other is called 'Impure Spectrum'.

Pure Spectrum : A Spectrum in which various bands of colours have sharp well defined boundaries and do not merge in each other is called 'Pure Spectrum'.

The angle through which light of particular wavelength can deviate, while passing through a prism is called 'Refrangibility'. The refrangibility for red light is least whereas for the violet light is maximum. 

Wavelengths of g - rays are ranging from 0.0001nm to 0.1 nm. (or) 0.001 A  to 1A⁰