An organ like the brain is considered to be a living thing, how is it possible?

The brain is an organ, and a very unusual and complex one at that. It plays a role in every one of our functions, controlling many organs, our thoughts, memory, speech, and movements.

Explanation:

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.