Question

Which among the following compounds show metal excess defect due to anionic vacancy?

• A. ZnO
• B. NaCl
• C. FeO
• D. CdO

Answer 1

The Correct Option is A

To determine which compound shows metal excess defect due to anionic vacancy, we need to examine the nature of defects in each option:

• ZnO: Upon heating, zinc oxide (ZnO) loses oxygen, resulting in an oxygen vacancy. Therefore, zinc ions (Zn²⁺) occupy interstitial sites, creating a metal excess defect due to anionic (oxygen) vacancies. 
• NaCl: Sodium chloride (NaCl) typically exhibits Schottky defects, not metal excess defects due to anionic vacancies.
• FeO: Iron(II) oxide (FeO) primarily demonstrates non-stoichiometry due to metal deficiencies rather than excesses.
• CdO: Like ZnO, cadmium oxide (CdO) can also exhibit metal excess defects due to anionic vacancies, but it is less common compared to ZnO.

Thus, ZnO is the compound that shows metal excess defect due to anionic vacancy.

Answer 2

To determine which compound displays a metal excess defect due to anionic vacancy, we need to understand the concept of defects in crystals:

Metal Excess Defect: This is a type of point defect in crystalline solids where there is an excess of metal ions. It can occur due to anionic vacancies or interstitial cations. In this case, we focus on anionic vacancies.

Anionic Vacancy: This type of defect occurs when an anion is missing from its lattice position, and the charge is compensated by extra electrons, often localized in the vacancy site, creating what is known as an F-center.

ZnO: When ZnO is heated, it can lose oxygen, resulting in Zn_1+xO_1-x. Oxygen vacancies in ZnO lead to extra Zn ions replacing the missing O^2- ions, leading to excess zinc ions and electrical conductivity due to extra electrons. This process is represented as:

O^2- → _Vacancy + 2e^-

This information indicates that ZnO exhibits a metal excess defect due to anionic vacancy.

Conclusion: Among the given options, ZnO is the compound that shows a metal excess defect due to anionic vacancy.