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Composition of the nuclei of two atomic species X and Y are given as under
 
 
X
Y
Protons66
Neutrons68
  
Give the mass numbers of X and Y. What is the relation between the two species?
Mass number = Protons +
Mass number of X = 
Mass number of Y =
As atomic number is equal to number of protons, the atomic number is same, i.e., 6.
Both X and Y are of same element.