Q No:17 How can determine the Pi electrons in Compound ??

Reasoning Question Series
Q No:17 How can determine the Pi electrons in Compound ??
Ans :
We can calculate the pi electron by
1. hybridization like 
sp3 compounds as CH4 = no pi electron
sp2 compounds as C2H4= 2 pi electrons
sp compounds as C2H2= 4 pi electrons
2. bond fromations
like
single bond = no pi electron
double bond = 2 pi electrons
triple bond = 4 pi electrons
3. index of Hydrogen deficiency (IHD)
its is also knowns as Degree of unsaturation
it is used to draw the chemical compounds forumula structure
IHD=2x+2−y/2
X= number of Carbon
y = number of hydrogen
if answer is one its mean it has one double bond
like
IHD for C2H4 is

2(2)+2−4/2=1
This means it can have either one double bond or one ring, but it cannot have a triple bond. Since you cannot form a ring with only two C’s, it must have a double bond.
4. Hucle Rule
with the help of huckle rule we can determine the pi electrons in aromatic compounds
4n+2 π electrons