How many 3-liter balloons could the 12-l helium tank pressurized to 160 atm fill? keep in mind that an "exhausted" helium tank is not empty. in other words, once the gas inside the tank reaches atmospheric pressure, it will no longer be able to fill balloons..

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 =

the answer is the index of refraction of the second medium is higher. i just took the test.