Hello!
To know how many moles of iron can be recovered from 100 kg of Fe₃O₄ we'll need to use the
molar mass of Fe₃O₄ and apply the conversion factor to go from kg of Fe₃O₄ to moles of Fe in the following way:

So, theoretically, one could recover
1192,68 moles of Fe from 100 kg of Fe₃O₄
Have a nice day!
B) the bacteria that live in the intestine of a rabbit
Is this a multiple choice? Anyways I will just give you a written answer and hopefully it helps.
A: Helium is made up of two electrons held by electromagnetic force to two protons that are inside of a nucleus along with one or two neutrons.
That's a ketone's functional group :)