Question

Why thallium has high ionization energy than indium ?

Answer 1

thallium's electrone layout is-6s^2 6p^1(outed chamber)
indium's electron layout of outed chamber is-5s^2 5p^1
because of greater chamber for thallium it needs more i.p to distract a electron and turn it into a positive ion(because of neuclius's high magnetivity)..

indium need less i.p