Transition elements form complex compounds primarily due to:

The spin only magnetic moment of $Mn^{4+}$ ion is nearly (in $BM$)

The transition elements have a characteristic electronic configuration which can be represented as:

Number of electrons present in $4f$ orbital of $Ho^{3+}$ ion is $.....$
(Given Atomic No. of $Ho=67$)

Assertion : Cuprous ion $(Cu^+)$ has unpaired electrons while cupric ion $(Cu^{2+})$ does not.
Reason : Cuprous ion $(Cu^+)$ is colourless whereas cupric ion $(Cu^{2+})$ is blue in the aqueous solution.

Which of the following statements is incorrect?