Answer:
option a) 3 g
Explanation:
mass of Glucose = 5 g
Mass of H₂O = ?
Reaction Given:
                    6CO₂ + 6H₂O ----> C₆H₁₂O₆ + 6O₂
Solution:
First we have to find mass of glucose from balanced reaction.
So, 
Look at the reaction
                         6CO₂ + 6H₂O -------> C₆H₁₂O₆ + 6O₂
                                      6 mol               1 mol
As 6 mole of water (H₂O) give 1 mole of Glucose (C₆H₁₂O₆ )
Convert moles to mass
molar mass of C₆H₁₂O₆  = 6(12) + 12(1) + 6(16)
molar mass of C₆H₁₂O₆  = 72 + 12 + 96 
molar mass of C₆H₁₂O₆= 180 g/mol
molar mass of H₂O = 2(1) + 16 = 18 g/mol
Now
              6CO₂      +  6H₂O          --------->     C₆H₁₂O₆   +    6O₂
                               6 mol (18 g/mol)           1 mol (180 g/mol)
                                   108 g                            180 g
 108 g of water (H₂O) produce 180 g of glucose (C₆H₁₂O₆)
So 
if 108 g of water (H₂O) produce 180 g of glucose (C₆H₁₂O₆) so how many grams of water (H₂O) will be required to produce 5 g of glucose (C₆H₁₂O₆).
Apply Unity Formula
                108 g of water (H₂O) ≅ 180 g of glucose (C₆H₁₂O₆)
                 X g of water (H₂O) ≅ 5 g of glucose (C₆H₁₂O₆)
Do cross multiply
                      mass of water (H₂O) = 108 g x 5 g / 180 g 
                      mass of water (H₂O) = 3 g
So 3 g of water is required to produce 5 g of glucose.