Density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is ρ (the lower case Greek letter rho), although the Latin letter D can also be used
The density of an object determines whether it will float or sink in another substance. An object will float if it is less dense than the liquid it is placed in. An object will sink if it is denser than the liquid it is placed in.
The water density anomaly is a concept in physics which describes a special phenomenon that characterizes the water: water in the solid state (ice) are less dense than liquid water. This is contrary to most solid-state materials.
I liked the question, it's especially relevant at this time when summer is approaching :)
The background gives the reader a good understanding of the knowledge required to answer the question. If I may suggest some ideas for improvement, I woud introduce some changes to the animation: it would be nice f you added music and made it a bit more dynamic...additonally, there's currently no connection between theanimation and the water anomaly mentioned in the text (other than a photo of ice cubes immersed in water). I would add some graphic explanation of the water anomaly in the animation, and it's physical princples, since it's a subject which is quite complex.