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Q.
$Ti ^{3+}$ transition metal ion is purple in colour while $Ti ^{4+}$ metal ion is colourless due to
AMUAMU 2011The d-and f-Block Elements
Solution:
Transitional metal ions having completely filled or empty d-orbitals,
ie, $(n-1) d^{10}$
or $(n-1) d^{0}$
configuration are colourless while transitional metal ions having $(n-1) d^{1-9}$
configuration are coloured due to $d - d$ transition.
$T i(22):[A r] 3 d^{2} A s^{2}$
$T i^{3+}:[A r] 3 d^{1} 4 s^{o}:$ purple
$T i^{4+}:[A r] 3 d^{0} 4 s^{o}:$ colourless
Hence, $T i^{4+}$ metal ion is colourless due to vacant d-orbitals.