Why does ice float instead of sink?

Because, unusually, solid ice is LESS dense than liquid water under standard conditions.

Usually the liquid phase is less dense than the solid phase. It happens that a given quantity of ice occupies more volume than the equivalent mass of water. And we've all seen the increase in volume when we make ice cubes in a freezer. Ice will therefore float.

How to remember this? Think Titanic!

Should ice be more buoyant in fresh water or salt water?