the density of water is 1gm/ml. what is the molarity of 1 drop of water?

Answer 1

Depends upon how many drops of water are in 1 mL. With a good teflon tipped buret, there are about 30 drops which makes each drop about 0.0333 mL.
That makes a drop have a mass of 0.0333 grams and that is 0.0333/18.015 moles or 0.00185moles/L or 0.00185/0.00003333 = 55.51 M which may be too many significant figures but you can take care of that.
I think a much easier route is to forget the 1 drop business. The molarity of 1 drop is the same as M of 10 drops or a L or a washtub of water.
1L H2O has a mass of 1000g (at the 1g/mL density level) and 1000/18.015 = 55.51 moles/L