Dear jyoti,
 In the case of antibonding molecular orbital, the electrons  try to go away from the nuclei and this corresponds to repulsive state.
The energy of this orbital will be higher. The relative energies of  bonding and antibonding molecular orbitals along with atomic orbitals  can be represented as shown in the figure given below.

fig 1.10 - Relative energies of s1s and s*1s molecular orbitals
Thus, the bonding molecular orbital is stabilized relative to the  energy of the isolated atoms and antibonding molecular orbital is  destabilized relative to the individual atoms. Further, it may be noted  that the bonding molecular orbital is stabilized to the same extent as  the antibonding molecular orbital is destabilized.
 







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