Match the properties given in List-I with the metals given in List-II…

The correct answer is Option (2) → (A)-(III), (B)-(I), (C)-(IV), (D)-(II)

The properties of the transition metals follow from their partly filled d orbitals. The number of unpaired d electrons decides the strength of metallic bonding (and so the melting point) and the range of oxidation states an element can show.

• (A) 3d series element with highest melting point — This matches (III) Cr. Cr (Z = 24) is \( \mathrm{[Ar]\,3d^{5}\,4s^{1}} \): six unpaired electrons all take part in metallic bonding, so the melting points of the 3d series reach their maximum at chromium (about d⁵).

• (B) element which can show +8 oxidation state — This matches (I) Os. Osmium, in group 8, uses all eight of its 5d and 6s electrons in \( \ce{OsO4} \), where it is +8; no 3d element reaches this state.

• (C) 3d series element with largest number of oxidation states — This matches (IV) Mn. Mn (Z = 25) is \( \mathrm{[Ar]\,3d^{5}\,4s^{2}} \); with seven electrons in these orbitals it shows every oxidation state from +2 to +7, the most in the series.

• (D) constituent of Mischmetall — This matches (II) Fe. Mischmetall is an alloy of a lanthanoid metal (about 95%) and iron (about 5%), with traces of S, C, Ca and Al; it is used in bullets, shells and lighter flints.

Shortcut: (A)-(III) and (B)-(I) are in Options (1) and (2); (C)-(IV) then leaves only Option (2).

NCERT (2026-27 edition):
Oxidation States – “The elements which give the greatest number of oxidation states occur in or near the middle of the series. Manganese, for example, exhibits all the oxidation states from +2 to +7.”

General Characteristics – “… A well known alloy is mischmetall which consists of a lanthanoid metal (~ 95%) and iron (~ 5%) and traces of S, C, Ca and Al.”