How can there be a sodium peroxide when the valency of Na is +1 and of O is -2. It will have to be Na2O

_{P2 O2+H2O-------->H3 PO4}

Is ripening of banana from green to yellow a chemical change ? 

 I can't understand the topic of 'determination of atomic mass'. Please explain how to calculate the atomic mass of an atom.

how to balance Fe (OH)₃ + H₂SO₄ = Fe₂ (SO₄)₃ + H₂O. what will the answer be?????....................