Number of electrons in the penultimate shell of $d-$block elements.

$3d-$ metal ions exhibit paramagnetic behavior because . . . . .

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

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

Which one of the following characteristics of the transition metals is associated with their catalytic activity?

What is the correct order of the theoretical magnetic moment for $Mn^{2+}$,$Cr^{2+}$,and $V^{2+}$?

Identify the alloy used for construction of gas turbine engines.