The vapour pressure of pure water at 25^oC is 30 mm. The vapour pressure of 10% (W/W) glucose  solution at 25^oC is :

10% solution contains 10 gms of glucose and 90 gms of water.

So, the amount of water in 90gm is equal to 90/18, or 5 moles.
Number of glucose moles equals 10/180 or 0.056 moles.
So, the total moles are 5 + 0.06 = 5.056 moles.
Water mole fraction = 5/5.056 = 0.988

final vapour pressure=P×X_water =30×0.980 =  29.67 mm.

Hence, the correct option (C). 29.67 mm