Considering the following statements; identify the correct statements…

Considering the following statements; identify the correct statements:

(A) Scandium is regarded as a transition element, but zinc is not.
(B) \( V_2O_3 \) is amphoteric and \( V_2O_5 \) is basic oxide.
(C) The similar radii of Zr and Hf is a consequence of the lanthanoid contraction.
(D) The oxidation state of chromium in chromate and dichromate ion is same.

Choose the correct answer from the options given below.

Answer & explanation

Correct answer: option 3

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

A transition element is one that has an incompletely filled d subshell in its ground state or in one of its common oxidation states. Down a group, the radii of the 4d and 5d elements become almost equal because of the lanthanoid contraction, and in the oxides of a metal the acidic character rises with the oxidation state.

(A) Scandium is regarded as a transition element, but zinc is not. — Correct. Sc (Z = 21) is \( \mathrm{[Ar]\,3d^{1}\,4s^{2}} \): a partly filled 3d subshell in the ground state. Zn (Z = 30) is \( \mathrm{[Ar]\,3d^{10}\,4s^{2}} \), and its only common ion, \( \ce{Zn^2+} \), is \( \mathrm{3d^{10}} \); the d subshell is full in both, so zinc is not regarded as a transition element.
(B) \( \ce{V2O3} \) is amphoteric and \( \ce{V2O5} \) is basic oxide. — Incorrect. It is the other way round. In \( \ce{V2O3} \) vanadium is +3 and the oxide is basic; in \( \ce{V2O5} \) vanadium is +5, the bonds are more covalent and the oxide is amphoteric, though mainly acidic.
(C) The similar radii of Zr and Hf is a consequence of the lanthanoid contraction. — Correct. Between Zr (4d series) and Hf (5d series) come the fourteen lanthanoids, whose 4f electrons shield the nucleus poorly. The size gained by adding a shell is cancelled, so Zr (160 pm) and Hf (159 pm) are almost the same size.
(D) The oxidation state of chromium in chromate and dichromate ion is same. — Correct. In \( \ce{CrO4^2-} \): \( x + 4(-2) = -2 \), so \( x = +6 \). In \( \ce{Cr2O7^2-} \): \( 2x + 7(-2) = -2 \), so \( x = +6 \). The two ions differ only in the pH at which they exist.

Considering the following statements; identify the correct statements:

Choose the correct answer from the options given below.

Answer & explanation

Correct answer: option 3

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

(A) Scandium is regarded as a transition element, but zinc is not. — Correct. Sc (Z = 21) is \( \mathrm{[Ar]\,3d^{1}\,4s^{2}} \): a partly filled 3d subshell in the ground state. Zn (Z = 30) is \( \mathrm{[Ar]\,3d^{10}\,4s^{2}} \), and its only common ion, \( \ce{Zn^2+} \), is \( \mathrm{3d^{10}} \); the d subshell is full in both, so zinc is not regarded as a transition element.
(B) \( \ce{V2O3} \) is amphoteric and \( \ce{V2O5} \) is basic oxide. — Incorrect. It is the other way round. In \( \ce{V2O3} \) vanadium is +3 and the oxide is basic; in \( \ce{V2O5} \) vanadium is +5, the bonds are more covalent and the oxide is amphoteric, though mainly acidic.
(C) The similar radii of Zr and Hf is a consequence of the lanthanoid contraction. — Correct. Between Zr (4d series) and Hf (5d series) come the fourteen lanthanoids, whose 4f electrons shield the nucleus poorly. The size gained by adding a shell is cancelled, so Zr (160 pm) and Hf (159 pm) are almost the same size.
(D) The oxidation state of chromium in chromate and dichromate ion is same. — Correct. In \( \ce{CrO4^2-} \): \( x + 4(-2) = -2 \), so \( x = +6 \). In \( \ce{Cr2O7^2-} \): \( 2x + 7(-2) = -2 \), so \( x = +6 \). The two ions differ only in the pH at which they exist.