Washing with water doesn't remove grease stains from clothes but addition of detergent removes the molecules of greasy substances. How can the coefficient of viscosity of a highly viscous liquid be determined by Stokes' method?

Washing with water doesn't remove grease stains from clothes but addition of detergent removes the molecules of greasy substances. Which property of liquid causes the above effect?

Washing with water doesn't remove grease stains from clothes but addition of detergent removes the molecules of greasy substances. A single drop of liquid is split into 8 identical drops. What will be the excess pressure in each drop?

Water from a river can't be used for washing clothes by soap. So people there are using detergents.Give reason for this and suggest a remedy.