Question

Unlike h3po4,h3po3 act as reducing agent

Answer 1

H3PO3 is a better reducing agent than H3PO4 . The reducing property of these acids are based on the no of hydrogen atoms bonded to the central metal atom .In the case of H3PO3 there is one P-H bond which is responsible for it's reducing character wherehas there is no such bonding in case of H3PO4.