$A$ transition element $X$ has a configuration $[Ar]3d^4$ in its $+3$ oxidation state. Its atomic number is

The least reactive metal is

Which statement is incorrect from the following?

Given below are two statements:
Statement-$I$: The first ionization enthalpy of $Cr$ is lower than that of $Mn$.
Statement-$II$: The second and third ionization enthalpies of $Cr$ are higher than those of $Mn$.
In the light of the above statements, choose the correct answer from the options given below:

How many unpaired electrons are there in $Ni^{2+}$?

The correct order of atomic/ionic radii is