Question

how does the density of water change at temperatures below 4°c? decreases increases

Explanation:

Water is anomalous as its density is maximum at 4°C. Below 4°C, as temperature drops, water molecules start to form a more open - structured lattice in preparation to freeze, and the volume increases. Since density $
ho=\frac{m}{V}$, with mass $m$ constant and volume $V$ increasing, density decreases.

Answer:

Decreases