Using 3 – 4 sentences explain (in your own words) why water expands when it freezes?

In the case of water, that is, when the liquid water gets cooled, it gets contract to a temperature of about 4 degrees is attained. However, after that, it starts to expand somewhat till it moves towards the freezing point, and eventually when it freezes, it expands by about 9 percent.  

This characteristic has its source in the composition of the water molecule. In water, there possesses a capacity to produce a network of hydrogen bonds, where each atom of hydrogen is in a line amongst the two atoms of oxygen. This tendency of hydrogen bonding gets robust as the temperature lowers down. The formed ice structure is completely hydrogen-bonded and these bonds permit the structure to get open, thus, expansion takes place.  

radioactive decay occurs in unstable atomic nuclei – that is, ones that don't have enough binding energy to hold

the nucleus together due to an excess of either protons or neutrons.

a rain shadow is a dry region of land on the side that is protected against the prevailing winds of a mountain range. the prevailing winds are the winds that occur most of the time in a particular place of the earth

prevailing winds carry air toward the mountain range. as the air rises up over a mountain range, the air cools, water vapor condenses, and clouds form. on this side of the mountains, called the windward side, precipitation falls in the form of  rain  or snow. this dry air produces a  rain shadow.