How do you calculate the molarity of a solution

Can someone me with questions 15 to 17 plz.

Phosphorous acid, h3po3(aq) , is a diprotic oxyacid that is an important compound in industry and agriculture. p k a1 p k a2 1.30 6.70 calculate the ph for each of the points in the titration of 50.0 ml of 1.5 m h3po3(aq) 1.5 m h 3 po 3 ( aq ) with 1.5 m koh(aq). 1.5 m koh ( aq ) .

Select the most likely product for this reaction: koh(aq) + co2(g) – ? k2co3(aq) + h2o(1) k(s) + h2(g) + o2(g) k(s) + co3(9) +h2