Which of the following statements about transition metals is true? a.
They are never found uncombined in nature.
b.
They include familiar metals such as gold, silver, copper, and nickel.
c.
They are so soft that they can be cut with an ordinary knife.
d.
They are the most reactive of all the types of metals.

b.They include familiar metals such as gold, silver, copper, and nickel.

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 =