How safe is dettol antiseptic solution when used daily for mopping marble floor?
It is not safe, it can damage marble. Marble is a soft stone. You could use dettol on granite and it would be fine, but I would not risk using it on marble. Mop the floor with a 4-chain ammonium chloride disinfectant. They are neutral ph and very mild. The kill claim should be far superior to the dettol.