By two or more atoms (chemically combined)
This balanced equation shows us the ratios of reactants and products, so for every 3 oxygen molecules, we see that 4 iron atoms react as well. The answer is 4.
The general fomula of the amine group ought to be R2NH because, the two hydrogen atoms of ammonia have been substituted by alkyl groups.
<h3>What is a secondary amine?</h3>
A secondary amine is one in which two alkyl groups are subtituted on the nitrohen atom of ammonia.
This implies that the general fomula of the amine group ought to be R2NH. This is because, the two hydrogen atoms of ammonia have been substituted by alkyl groups.
Learn more about secondary amine: brainly.com/question/12682525
C. Ninhydrin is used to detect prints on a non-porous surface