Question

the surface of rivers freeze when the temperatures falls below freezing. however, the water underneath this layer of ice continues to flow. this phenomenon allows fishermen to fish through holes drilled in the ice the entire winter. which property of water is the reason the river doesnt freeze completely?

cohesion holds the water molecules together.
density of 1.0
water is an excellent solvent.
hydrogen bonds expand during the freezing process.

Explanation:

When water freezes, hydrogen - bonds cause the water molecules to arrange in a lattice structure that is less dense than liquid water. Ice is less dense than liquid water, so it floats on the surface. This floating ice layer insulates the water below, preventing the river from freezing completely.

Answer:

Hydrogen bonds expand during the freezing process.