Why dielectric constant of water decreases as ice is formed?

Answer 1

You're not quite right. The dielectric of the solid (ice) is HIGHER than the dielectric of the liquid (water).

Although water has a reasonably high dielectric constant (because the water molecule has a dipole moment and so water can be polarized to virtually eliminate the field's effect), it still can act as a conductor because it always contains ions (OH- and H+ are always there, and also things like Cl- and Na+ are usually present) which are highly mobile.

Being conducting means that there is a current present whenever you apply an electric field, and the current means you have charge "leaking". Yes, the reason water conducts well is because it is liquid, so ice is not a good conductor (though ice with a layer of liquid water on the outside would still probably allow quite a bit of current to flow).

In ice the water molecules have all lined themselves up in a fixed structure where the hydrogen bonds can be maximally satisfied. This means the dielectric relaxation time is higher, and the molecules can't realign themselves to a changing electric field easily. This corresponds to a higher observed dielectric constant.

Answer 2

Dielectric Constant Of Ice

Answer 3

The density decreases.