Correct Answer – B
The d-block metals are less reactive than s-block metals. However, many of the metals are sufficiently electropositive to react with mineral acids, liberating `H_(2)`. A few have low standard electrode potentials and remain unreactive or noble. Except in the ususual circumstances, metals act only as reducing agents. Generally, the reactivity of the d-block metals as reducing agents tends to decreases as we go across the periodic table form left to right. The trend in thier reactivity can be related to their electrode potentoials. Group 3 metals including lanthanides and actinides are strong reducing agents. The metals of Groups 4-7 are moderately reactive as are Fe, Ru, Os, Co and Ni of Groups 8 to 10. The remaining metals of Groups 8-10, Rh, Ir, Pt and Pd, as well as Ag and Au have low reactivity. Hence, they are called noble metals. Noble character is favoured by (i) high enthalpies of sublimation, high ionization ehthalpies and low enthalpies of solvation. The high melting points lead to high enthalpies of solvation. The smaller atoms result in high ionization enthalpies. This tendency top noble character is most pronounced for the platinum metals (Ru, Rh, Pd, Os, Ir, Pr) and gold.