Out of the following given statements, identify the correct ones: (A)…

Out of the following given statements, identify the correct ones:

(A) Yttrium does not exhibit variable oxidation states, yet it is a transition element.
(B) Many compounds of transition elements act as catalysts in various chemical reactions.
(C) Technetium is an artificially synthesized element of 4d transition series.
(D) The E° value for the \( Mn^{3+}/Mn^{2+} \) couple is much more positive than that for \( Cr^{3+}/Cr^{2+} \)

Choose the correct answer from the options given below:

Answer & explanation

Correct answer: option 3

The correct answer is Option (3) → (A), (B), (C) and (D)

A transition element is one that has an incompletely filled d subshell in its atom or in its common ions. Their typical properties, such as catalytic activity and the relative stability of oxidation states, follow from the d electrons.

(A) Yttrium does not exhibit variable oxidation states, yet it is a transition element. — Correct. Y (Z = 39) is \( \mathrm{[Kr]\,4d^{1}\,5s^{2}} \). It shows only the +3 state, but its atom has an incomplete 4d subshell, so it is a transition element; variable valency is common, not a requirement.
(B) Many compounds of transition elements act as catalysts in various chemical reactions. — Correct. Their variable oxidation states and ability to form complexes make them good catalysts, for example \( \ce{V2O5} \) in the contact process and finely divided iron in the Haber process.
(C) Technetium is an artificially synthesized element of 4d transition series. — Correct. Tc (Z = 43) lies between Mo and Ru in the 4d series. It has no stable isotope and was the first element to be made artificially.
(D) The E° value for the \( \ce{Mn^{3+}} \)/\( \ce{Mn^{2+}} \) couple is much more positive than that for \( \ce{Cr^{3+}} \)/\( \ce{Cr^{2+}} \) — Correct. E°(\( \ce{Mn^{3+}} \)/\( \ce{Mn^{2+}} \)) is +1.57 V and E°(\( \ce{Cr^{3+}} \)/\( \ce{Cr^{2+}} \)) is −0.41 V. Mn (Z = 25) is \( \mathrm{[Ar]\,3d^{5}\,4s^{2}} \), so \( \ce{Mn^2+} \) is \( \mathrm{3d^{5}} \), a stable half-filled set, and \( \ce{Mn^3+} \) is readily reduced to it. Cr (Z = 24) is \( \mathrm{[Ar]\,3d^{5}\,4s^{1}} \), so \( \ce{Cr^3+} \) is \( \mathrm{3d^{3}} \), stable with a half-filled t_2g set, and \( \ce{Cr^2+} \) is readily oxidised to it.

Out of the following given statements, identify the correct ones:

Choose the correct answer from the options given below:

Answer & explanation

Correct answer: option 3

The correct answer is Option (3) → (A), (B), (C) and (D)

(A) Yttrium does not exhibit variable oxidation states, yet it is a transition element. — Correct. Y (Z = 39) is \( \mathrm{[Kr]\,4d^{1}\,5s^{2}} \). It shows only the +3 state, but its atom has an incomplete 4d subshell, so it is a transition element; variable valency is common, not a requirement.
(B) Many compounds of transition elements act as catalysts in various chemical reactions. — Correct. Their variable oxidation states and ability to form complexes make them good catalysts, for example \( \ce{V2O5} \) in the contact process and finely divided iron in the Haber process.
(C) Technetium is an artificially synthesized element of 4d transition series. — Correct. Tc (Z = 43) lies between Mo and Ru in the 4d series. It has no stable isotope and was the first element to be made artificially.
(D) The E° value for the \( \ce{Mn^{3+}} \)/\( \ce{Mn^{2+}} \) couple is much more positive than that for \( \ce{Cr^{3+}} \)/\( \ce{Cr^{2+}} \) — Correct. E°(\( \ce{Mn^{3+}} \)/\( \ce{Mn^{2+}} \)) is +1.57 V and E°(\( \ce{Cr^{3+}} \)/\( \ce{Cr^{2+}} \)) is −0.41 V. Mn (Z = 25) is \( \mathrm{[Ar]\,3d^{5}\,4s^{2}} \), so \( \ce{Mn^2+} \) is \( \mathrm{3d^{5}} \), a stable half-filled set, and \( \ce{Mn^3+} \) is readily reduced to it. Cr (Z = 24) is \( \mathrm{[Ar]\,3d^{5}\,4s^{1}} \), so \( \ce{Cr^3+} \) is \( \mathrm{3d^{3}} \), stable with a half-filled t_2g set, and \( \ce{Cr^2+} \) is readily oxidised to it.