Question

The concentration of solution containing 0.5 mole H3PO, dissolved in 500 g water

Answer 1

I think you mean H3PO3 or H3 PO2

As u have not mentioned the compound I cannot solve it but I'll tell you how to do it

Moles= weight /molwt

0.5×mol.wt=weight

I hope this helps ( ╹▽╹ )