Question

write a balanced equation for phosphorous burns in oxygen to form phosphorous pentoxide.

Answer 1

The general equation is

P4+O2→P2O5
Actually phosphorus is a polyatomic substance. Its atomicity is 4
Here for the formation of 1 P2O5 molecule 2 – phosphorus atoms, 5- oxygen atoms are required.
Therefore   4- phosphorus atoms will form 2 P2O5molecules.
For the formation of 2 P2O5 molecules 10 oxygen atoms are required.
For balancing the equation keep 5 in front of O2molecule
 P4+5O2→P2O5

Answer 2

When 4 mole of phosphorus burns with 5 mole of oxygen, it gives 2 mole of P2O5.

4P +5 O2 ==> 2P2O5

But when white phosphorus reacts with oxygen at 50℃ it gives 1 mole of P4O10.

4P + 5O2 ===> P4O10