On a summer day, 175 000 joules of energy are supplied to this electric aircraft's solar cells every second. The useful energy transferred by the solar cells is 35 000 joules every second.
Calculate the efficiency of the solar cells.

float.

archimedes' principle

denser than water sinks in water.

denser than mercury would sink in it

there are no contact forces mentioned on the list of choices that you've provided.

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 =