Order of First Ionisation Enthalpy of Boron or 13th Group

B > Tl > Ga > Al > In ( IE1- Order)

Size of isoelectronic Species/ions decrease with increasing in atomic number or protons.

For transition elements – There are four series of transition elements

3d – Sc (21) to Zn (30)

4d – Y (39) to Cd (48)

5d – La (57), Hf (72) to Hg (80)

6d – Ac(89), Rf(104) …………. Unb (ununbium) 112 (incomplete)