Phosphorus reacts with oxygen to produce different kinds of oxides. One of these oxides is formed when 1.347 g of
phosphorus reacts with 1.744 g of oxygen. What is the
simplest formula of this oxide?

check below

Explanation:

You can find the empirical formula of phosphorus oxide

  P                         O

1.347g                  1.744

1.347/ 31            1.744/ 16

0.043                  0.109

0.043/ 0.043   0.109/ 0.043

1                     :        2.5

2                    :         5

P2O5