Boron forms no compounds in unipositive state but thallium in unipositive state is quite stable. explain

Boron shows only +3 oxidation state whereas Thallium shows both +1 & +3 oxidation state.
Hope this will clear your doubt.

This may be due to inert pair effect as when an electron is get ejected from Boron as1s^2 2s^2 2p^1 when this electron leaves from 2p orbital then it gets inert and will not participate in any reaction and hence form no compounds.

Boron has electronic configuration 2 s^22p^1 .It always trivalent in its compounds.on the other hand boron prefers to form unipositive ion, rather than tripositive ion .In case of thallium it has electronic configuration 6s^26p^1 .The outermost 6s^2 electrons do not take part in bonding and behave like inert gas . Therefore, thallium forms compounds in unipositive State.