Number of unpaired electrons in $Mn^{4+}$ is

In which of the following cases,the stability of two oxidation states is correctly represented?

What are the $d-$block elements in the modern periodic table known as?

Which of the following transition elements have nearly the same atomic radii?

In what way is the electronic configuration of the transition elements different from that of the non-transition elements?

Match the metal ions given in Column-$I$ with the spin magnetic moments of the ions given in Column-$II$ and assign the correct code.

Column-$I$	Column-$II$
$(a) \ Co^{3+}$	$(i) \ \sqrt{8} \ B.M.$
$(b) \ Cr^{3+}$	$(ii) \ \sqrt{35} \ B.M.$
$(c) \ Fe^{3+}$	$(iii) \ \sqrt{3} \ B.M.$
$(d) \ Ni^{2+}$	$(iv) \ \sqrt{24} \ B.M.$
	$(v) \ \sqrt{15} \ B.M.$

$(a) \quad (b) \quad (c) \quad (d)$