Aromatic compound has continuous cyclic structure with( 4n+2)π electrons (Huckels rule), where n = 0,1,2…
Here number of pi electron are 6, where 4 from two double bond and 2 from nitrogen non-bonding electrons, hence it has total 6 pi electrons, therefore
6= ( 4n+2)π
4 = 4n
n =1
Hence it is an aromatic compound
Answer:
Three hydrogen atoms to form PH₃.
Explanation:
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In this case, since the elements belonging to the nitrogen family (N, P, As, Sb and Bi) show five valence electrons, because there are five electrons at their outer shell, it is clear that if phosphorous bonds with hydrogen, it is going to require the same amount of oxygen atoms (3) because elements having five valence electrons need 3 bonds in order to attain the octet (5+3=8).
Therefore the compound would be:

Which is phosphine.
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Oxygen is the 8th element in the periodic table. This means that oxygen has 8 protons<span> and 8 electrons. In order to get the number of neutrons you take the atomic weight in this case 15.9999~16 and you subtract it by the number of protons (16-8) (o_O)
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The element symbol in chemistry comprises atomic number and mass number.
Atomic number is written on the top of element and mass number is written at the bottom.
For eg:
If Y is an element that is having atomic number a and mass number x. Then its denotion will be:
ᵃYₓ.
So here ⁹F₁₈.₉₉
Here 18.99 will denote mass number while 9 will denote atomic number.