Briefly explain the importance of optimal fluoride concentrations in drinking water. at which point during the water purification process should fluoride be added to the water? (6) what is the reason for adding fluoride at this particular stage? a home water softener has 75 000 cm3 of ion exchange resin with a capacity of 39 kg/m3. 3.3 the occupants use 1800 l/day of water containing 0.24 mg/cm3 of hardness as cacoa. if they want to soften the water to 78 mg/l as caco3, what percentage of water should bypass the unit? when will the unit need to be regenerated?

The answer for this question is d. none of these

1. why does the same side of the moon always face earthc.the rotational period of the moon is equal to one revolution around earth2. which is greater the moons period of rotation or its period of revolution  b.the moons revolution period around earth3.what was the major accomplishment of the apollo missions  d.landing on and exploring the moon4. which of these space missions involved the deployment of lunar rovers d.apollo5. which scientists are going to explore next on kepler-186fd. evidence of existence of life6.which mission is not going to explore the outside of the solar systemb.safir7.which technology limit the future of space exploration b. scientist must first develop certain technologies before missions can be completed.