Answer:
1st step : find the number of moles for the known substance
number of moles =mass/ relative molecular mass
n=23/Li2O2
n=23/(14+32)
n =23/46
n= 0,5moles
2nd step : balance the equation
2Li202 +2H20-----> 4LiOH +O2
3rd step : find the mole ratio of the known or stated using the balanced equation
Li2O2 : O2
2 : 1
4th step :find the number of moles for the asked using the mole ratio using simple proportion
Li2O2 :O2
2 :1
0,5 :???
0,5/2 ×1
= 0,25moles for (O2)
5th step : find the asked either mass , volume , concentration
number of moles = volume/molar gas volume
volume = number of moles × molar gas volume
v = 0,25moles × 28dm^3
v= 7 dm^3 of (O2)