One mole of methanol, when burnt in oxygen, gives out 723 KJ  heat. If one mole of oxygen is used, the amount of heat evolved is

 The reaction of combustion of methane is given below:

${\mathrm{CH}}_3\mathrm{OH}\left(\mathrm{g}\right)+\frac{3}{2}{\mathrm{O}}_2\to {\mathrm{CO}}_2+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$ 

The enthalpy for this reaction will be 723 KJ. 

When 1.5 moles of oxygen is used then 723 KJ is released. So, for 1 mole of oxygen the enthalpy will be:

$\mathrm{Enthalpy}=\frac{723}{1.5}=482\text{ KJ}$ 

So, the enthalpy will be 482 KJ.

Therefore, the correct option is C.