Astudy from the national institutes of health states that the human body contains trillions of microorganisms that make up 1% to 3% of the body mass. use this information to estimate the average mass of the body's approximately 100 trillion microorganisms

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 =

less than one you can't create energy

the answer is b, have negligible mass