For H3PO3 and H3PO4, the correct choice is

H3​PO3​ is a dibasic acid as it has 2 number of replaceable OH groups(Dibasic) attached to phosphorous. The oxyacids of phosphorous are reducing agents.H3​PO3​ is a good  reducing agent than H3​PO4​ . The reducing nature of these acids is based on the no of hydrogen atoms bonded to the central metal atom. As more number of H attached to phosphorous more is its reducing nature. In the case of H3​PO3​, there is one P−H bond which is responsible for it's reducing character whereas there is no such bonding in case of H3​PO4​.