Niobium $(Nb)$ and ruthenium $(Ru)$ have " $x$ " and " $y$ " number of electrons in their respective $4d$ orbitals. The value of $x+y$ is $...........$

Identify the incorrect statement in the following.

Identify the metal that forms colourless compounds.

The lanthanide contraction is responsible for the fact that

Total number of $d$ electrons present in an element with atomic number $78$ is:

The spin-only magnetic moment value of the ion among $Ti^{2+}$,$V^{2+}$,$Co^{3+}$,and $Cr^{2+}$ that acts as a strong oxidizing agent in aqueous solution is .......... $BM$ (nearest integer).
(Given atomic numbers: $Ti = 22, V = 23, Cr = 24, Co = 27$)