Which element belongs to the $d-$block?

Why is $_{21}Sc$ not considered a transition element?

The thermodynamic stability of transition metal elements is based on which of the following?

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 pairs of elements cannot form an alloy?

How is the variability in oxidation states of transition metals different from that of the non-transition metals? Illustrate with examples.