Gel/space ratio is defined as the ratio of the volume of the hydrated cement paste to the sum of volumes of the hydrated cement and of the capillary pores. It relates strength more correctly than water/cement ratio. Theoretical Strength = 240 × (gel/space)‌3 ; where 240 represents the intrinsic strength of the gel in MPa for the type of cement and specimen used. = 240 × (0.65)‌3 = 65.91 % or 0.65, Hence select closest correct answer i.e 0.678