Two H atoms in the ground state collide in-elastically. The maximum amount by which their combined kinetic energy is reduced is
As we know, Energy in the ground state (n=1) is E
where Z is atomic number so for energy of two H-atoms in the ground state, whose atomic number is Z=1, the energy will be twice , i.e.
.
After the inelastic collision between two H-atoms, one of the H-atom should go into first excited state (n=2) so that maximum amount of combined kinetic energy can be reduced. In other words the total energy of two H-atoms after inelastic collision will be
E=Ground state energy + Excited state energy
E
[∵ for H-atom Z=1]
E
[∵ for 1st excited state n=2]
E
Now loss in K.E due to inelastic collision will be the maximum amount of combined kinetic energy reduced
i.e. 
Therefore option (a) is correct.