10.2g of pure hydrogen peroxide are strongly heated till completely decomposed. calculate the volume of oxygen evolved at 27 degree Celsius and 740 pressure .please answer this soon before 16 September

Dear student

First of all the balanced chemical equation is to be written.   

                        2H₂O₂ ----------- 2H₂O + O₂(g)
Initially  10.2/34= 0.3 mol         -            -

Finally                   -                        0.3 mol    0.15 mol

Here we need to make use of the mole concept and the stiochiometry of the reaction. 
Now considering all the hydrogen peroxide will get consumed and also that the water so formed will be in liquid state and considering the ideal gas equation for oxygen 
we get
PV = n RT
740 mm Hg * V = 0.15 mol * (0.0821 L *760 mm Hg /K/mol )*300K
​we get Volume as = 3.79 L

Regards