geometry is sp3d and no. of lone pairs is 2 therefore shape is T shaped
( Br has 7 electron and 3 are bonded with 3 methyl group so it has 4 e i.e. 2 lone pair therefore it has 5 molecular orbtal which accounts for sp3d geometry)
for no. of empty orbital :
Br has 16 orbital in its valence shell (1s 3p 5d 7f)
and electron present in these orbitals are : 2 in s , 5 in p and d & f are empty
and when bonding with methyl groups occurs 1 electron from p orbital of Br transit to empty d orbital for bonding with methyl groups
(in all 3 electrons for bonding 2 in p and 1 in d) that leaves 2 lone pair
which results in 11 empty orbitals ( 4 in d and 7 in f )
