Acids containing oxygen are called oxyacids. Prefix 'Pyro' is used when two units of a parent acid condense together with removal of one water molecule. When one unit of a parent acid on an average loses a water molecule producing an acid having at least one acidic hydrogen, the resulting acid is called meta-acid.

${\mathrm{H}}_4{\mathrm{P}}_2{\mathrm{O}}_8$ Has :