Name a transition element which does not exhibit variable oxidation states.

An element with atomic number $21$ is a

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 $E^{o}_{M^{3+} / M^{2+}}$ value?

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 group of elements is known as coinage metals?

Which among the following elements is a soft element as compared to others?