Hello

It is quite easy dear, first of all let us write the chemical reaction which takes place when SiO2 reacts with Fe3O4 ,

SiO2 + 3Fe3O4 -> 2Fe3O4 + SiO2+1/2O2.


Now ,as per  the question we know that the reactant will have total mass of 2g and the Fe3O4 + SiO2 is having weight 1.96g and thus the weight of the oxygen will be 0.02g.


3 moles of Fe3O4 will give 1/2O2.


Thus, 1 O2 will give 3x160/16( molar mass of Fe3O4=160g and O2 is 32g).


So, 1 O2 will be 30 moles so 0.04 will give 30x0.04 = 1.2g.


So, the mass of SiO2 will be (2-1.2)g = 0.8g.


Thankyou