Carly has discovered a new radioactive isotope: unicornium-210. Based on atomic mass alone, into which of the following elements could 210 Ui not decay?
A-1515m
B-238U
C-90Sr
D-115EU

neither accurate nor precise.

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 =