The number of unpaired electrons in Gadolinium $[Z = 64]$ is

Identify the order in which the spin-only magnetic moment (in $BM$) increases for the following four ions:
$(I) Fe^{2+}$
$(II) Ti^{2+}$
$(III) Cu^{2+}$
$(IV) V^{2+}$

Those elements whose two outermost orbitals are incompletely filled with electrons are known as:

In context with the transition elements,which of the following statements is incorrect?

Which element from the following in $+3$ oxidation state forms colourless compounds?

Assertion : $E^o$ for $Mn^{3+}/Mn^{2+}$ is more positive than $Cr^{3+}/Cr^{2+}$.
Reason : The third ionization energy of $Mn$ is larger than that of $Cr$.