Ionisation energy of he+ is 19.6 multiplied by 10^-18, The energy of the First stationary state (n=1) of LI+2 is

Use equation:

E=hcR(1/n1^2–1/n2^2)Z^2

where E is energy, c and R are constant, Z IS ATOMIC NUMBER

So for a particular transition in He(Z=4), Energy is 19.6x10^-18(say A),

the energy for the same transition in lithium(z=3) would be,

A*3^2/2^2=9A/4

so energy for Li+2 transition will be 9*19.6*10^-18/4=44.1*10^-18J per atom

Approved