Oxygen can be obtained from water using electrolysis process as follows:
2 H2O .............> 2H2 + O2
It is given that: 
molar mass of water = 10.01 grams and molar mass of O2 = 32 grams
From the balanced chemical equation, we can conclude that:
2 moles of water produce 1 mole of oxygen
2 x 18.01 = 36.02 grams of water produce 32 grams of oxygen.
To calculate how many grams of water must react to produce 50 grams of oxygen, we can use cross multiplication as follows:
mass of required water = 56.28125 grams
        
             
        
        
        
Answer:
12 %
Explanation:
Produces 15 J of work for input 125 J
15/125 * 100% = 12% 
 
        
             
        
        
        
According to Raoult's low:
We will use this formula: Vp(Solution) = mole fraction of solvent * Vp(solvent)
∴ mole fraction of solvent = Vp(Solu) / Vp (Solv)
when we have Vp(solu) = 25.7 torr & Vp(solv) = 31.8 torr 
So by substitution:
∴ mole fraction of solvent = 25.7 / 31.8 =0.808 
when we assume the moles of solute NaCl = X 
and according to the mole fraction of solvent formula:
mole fraction of solvent = moles of solvent / (moles of solvent + moles of solute)
by substitute:
∴ 0.808 = 0.115 / (0.115 + X)
 So X (the no.of moles of NaCl) = 0.027 m