In the attachment there is a density column where there is colour Question: tell me why is the red at the bottom of the density column if it is the least dense

For your kind information, read the question thoroughly!

The bottom is the container part and not the liquid.

I hope it will be useful.

The star is pink. Pink is the MOST dense on the list.

The red thing below the star is the foot of the tube that all the liquids and the star are in.

it is given that trillions of microbes make up to 1% to 3% of the body mass.

let's take average of this percentage: 2%

consider the average mass of the human body as 70 kg.

then, trillions of microbes would have mass  

therefore, 100 trillion micro-organisms would weigh:

this is an approximate value and could change depending on the mass of the human body and percentage of the microbes present in it.

average mass per microorganism =