An unknown element ' X ' belongs to the 5 d transition series. It is observed that ' X ' has an atomic radius almost identical to the element ' Y ' directly above it in t

Question

An unknown element ' X ' belongs to the 5 d transition series. It is observed that ' X ' has an atomic radius almost identical to the element ' Y ' directly above it in the 4d series. Which of the following statements regarding ' X ' and ' Y ' must be correct?

TestHub · Accepted Answer

Concepts: Lanthanide Contraction, Ionization Energy trends in d-block, Density ( $ρ = ma ss / v o l u m e$ ), Electronegativity.

Solution:

1. Radius: Identical radii in 4d/5d pairs (like Zr/Hf, Nb/Ta, Mo/W) are due to Lanthanide Contraction. (A) is correct.

2. Ionization Energy: Usually, IE decreases down a group. However, for 5d elements, because of the Lanthanide Contraction, the valence electrons are held very tightly by the high $Z_{e ff}$ . Thus, IE₁ of 5d elements is often higher than 4d elements. (B) is correct.

3. Density: Density $ρ = ma ss / v o l u m e$ . X and Y have nearly the same volume (since radii are similar), but the atomic mass of X (5d) is nearly double that of Y (4d). Therefore, the density of X is roughly twice that of Y. (C) is correct.

4. Electronegativity: X has a very high $Z_{e ff}$ due to poor shielding of 4f. This makes it more electronegative than expected, often higher than Y. (D) is incorrect.

Correct Answer: (A), (B), (C)

Chemistry - Complete d-block Question with Solution | TestHub

Options:(select one or more)

Doubts & Discussion