A student walked 2 kilometers in 30 minutes. What was their average speed in kilometers per hour?

whichever one it is, it's definitely not one that you included on the list you provided.

no

sodium is solid at rt

what is the actual question though?

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 =