N-N single bond enthalpy is 'X'  N=N double bond enthalpy is 'Y' correct relation is

$\stackrel{∙∙}{\mathrm{N}}-\stackrel{∙∙}{\mathrm{N}}$

sigma bond is very weak due to the repulsions between the adjacent nitrogen atoms

  $∴$ 'X' has very low magnitude

A double bond contains one sigma (strong) and a Pi-bond(weak)

So  Sum of enthalpies of two sigma bonds > Enthalpy of a Double bond

But in the case of Nitrogen

Sum of enthalpies of two sigma bonds (2X)< Enthalpy of a Double bond(Y)

                2X < Y