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Nilanjan Bhowmick AIR 3, CSIR NET (Earth Science)
Suman Kumar
Use this simple formula If n=period number x=number of electrons in one orbit Number of elements in nth period= x*{(n+2)/2}^2 if n is even
x*{(n+1)/2}^2. if n is odd
Now Here n= 9.
3*((9+1)/2)^2 = 75