I think there is 3 moles of carbon atoms in 3 moles of methane. This is so as the chemical formula for methane is CH4, which means that for every 1 mole of methane molecule you have 1 mole of carbon atom as in each molecule of methane there's one carbon atom.
Significant figures let you, and other people looking at your results know how accurate your measurement is.
Hope this helps :)
The answer is. :
nitrogen has 1s2 2s2 2p3 electronic configuration... it still needs 3e' to get octet structure and become stable.. hence valency=3.
ANSWER:
A. n=5 to n=1
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