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Q.
Element with atomic number $81$, is present in which block?
Punjab PMETPunjab PMET 2009
Solution:
The electronic configuration of the atom with atomic number $81$ is
$=[ Xe ] 4 f^{14},\, 5 d^{10},\, 6 s^{2} p^{1}$
Electronic configuration shows that $p$ orbitals of the element are incomplete, hence it belongs to $p$ block (III A group element, ie, Tl).