Newton's third law of motion states that if a force is exerted on an object, another force occurs that . A.

is in the same direction and speed
B.

is in the same direction and size
C.

is equal in speed and opposite in direction
D.

is equal and opposite in direction

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 =