Match the properties given in List-I with the metals given in List-II
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List-I (Property) |
List-II (Metal) |
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(A) An element which can show +8 oxidation state |
(I) V |
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(B) 3d block element that can show upto +7 oxidation state |
(II) Cr |
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(C) 3d block element with the highest melting point |
(III) Os |
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(D) 3d block element with the highest enthalpy of atomization |
(IV) Mn |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A)-(III), (B)-(IV), (C)-(II), (D)-(I)
In the transition elements both the (n−1)d and the ns electrons take part in bonding. This gives them variable oxidation states, up to the total number of these electrons, and strong metallic bonding, which raises their melting points and enthalpies of atomisation; these are highest in the middle of each series, where the number of unpaired d electrons is large.
(A) An element which can show +8 oxidation state — This matches (III) Os. Osmium (Z = 76), \( \mathrm{[Xe]\,4f^{14}\,5d^{6}\,6s^{2}} \), can use all eight 5d and 6s electrons, as in \( \ce{OsO4} \). No 3d element reaches +8.
(B) 3d block element that can show upto +7 oxidation state — This matches (IV) Mn. Manganese (Z = 25), \( \mathrm{[Ar]\,3d^{5}\,4s^{2}} \), has seven 3d + 4s electrons; it shows +7 in \( \ce{KMnO4} \) and \( \ce{Mn2O7} \).
(C) 3d block element with the highest melting point — This matches (II) Cr. Chromium (Z = 24), \( \mathrm{[Ar]\,3d^{5}\,4s^{1}} \), has six unpaired electrons for metallic bonding and a very high melting point (about 2180 K), at the top of the 3d series together with vanadium.
(D) 3d block element with the highest enthalpy of atomization — This matches (I) V. Vanadium (Z = 23), \( \mathrm{[Ar]\,3d^{3}\,4s^{2}} \), has the highest enthalpy of atomisation of the series, 515 kJ mol−1 (Cr is 397 kJ mol−1).
Shortcut: (B)-(IV) appears in Options (1) and (2); (D)-(I) then leaves only Option (2).