Which of the following metals make the most efficient catalyst?

The metal ion which does not form coloured compounds is

Which of the following statements about the interstitial compounds is incorrect?

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 of the following sets correctly represents the increase in the paramagnetic property of the ions?

Which element from the following does $NOT$ exhibit a spin-only magnetic moment in the $+3$ oxidation state?