For naming the oxo-acids of phosphorus , the prefix 'pyro' is used for

Question

$\begin{array}{1 1} \text{The acid obtained by loss of H_2O Molecules } \\ \text{The acid having lower oxygen content than the parent acid } \\ \text{the acid obtained from two molecules with the loss of water molecules } \\ \text{the substance obtained on heating the acid }\end{array}$