Binding energy per nucleon versus mass number curve for nuclei is shown in the fig. W, X, Y and Z are four nuclei indicated on the curve. The process that would release energy is

 

For release of energy, 

${\mathrm{BE}}_{\mathrm{Product}}>{\mathrm{BE}}_{\mathrm{Reactant}}$

${\mathrm{BE}}_{\mathrm{W}}=120\times 7.5=900 \mathrm{MeV}$

${\mathrm{BE}}_{\mathrm{X}}=90\times 8.0=720 \mathrm{MeV}$

${\mathrm{BE}}_{\mathrm{Y}}=60\times 8.5=510 \mathrm{MeV}$

${\mathrm{BE}}_{\mathrm{Z}}=30\times 5.0=150 \mathrm{MeV}$

For $\mathrm{W}\to 2\mathrm{Y}$,

B.E. of reactants = 120(7.5) = 900 MeV
B.E of products = 2(60)8.5 = 1020 MeV

Hence, this energy is released in this process.

In other given processes, 

${\mathrm{BE}}_{\mathrm{Product}}<{\mathrm{BE}}_{\mathrm{Reactant}}$