Four successive members of the first row transition elements are listed below with their atomic numbers. Which one of them is expected to have the highest third ionization enthalpy?

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A)$: The first ionization enthalpy of $3d$ series elements is more than that of group $2$ metals.
Reason $(R)$: In $3d$ series of elements,successive filling of $d$-orbitals takes place.
In the light of the above statements,choose the correct answer from the options given below:

Which of the following transition metal ions has a definite magnetic moment?

Why is $Cr^{2+}$ reducing and $Mn^{3+}$ oxidising when both have $d^{4}$ configuration?

If $A$ is $[Rn]\,6d^2\,7s^2$,then identify the block,period,and group.

The lanthanide contraction is responsible for the fact that