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.

Which of the following is correct for ${\mathrm{H}}_3{\mathrm{P}}_3{\mathrm{O}}_9$?