Species having an X-O-H linkage, where X is a non-metal with a positive oxidation state, are called oxyacids. A parent oxyacid of a non-metal may exist in two forms: (a) the −ic form and (b) the −ous form.
Which of the following parent oxyacids does not have a pyro-oxyacid?
(1) H2SO3
(2) HNO3
(3) H3PO3
(4) H4SiO4