Question

Among the following, which species represents a pseudohalide?

• A. CN$^-$
• B. CaO
• C. I$_2$
• D. K$_2$HgI$_4$
• E. BiOCl

Hint:

Common pseudohalides include $CN^-$ (cyanide), $OCN^-$ (cyanate), and $SCN^-$ (thiocyanate). They are often referred to as "honorary halides."

Answer 1

The Correct Option is A

Concept: Pseudohalides are polyatomic functional groups that mimic the chemical behavior of true halide ions ($F^-$, $Cl^-$, $Br^-$, $I^-$).

Step 1: {Analyze the properties of the cyanide ion ($CN^-$).}
The $CN^-$ ion behaves similarly to halides in many ways: it forms a dimeric molecule (cyanogen), creates insoluble salts with silver ($AgCN$), and forms a weak hydracid ($HCN$).

Step 2: {Compare with other given options.}
Other species like $CaO$ (oxide), $I_2$ (true halogen), and complex salts do not meet the criteria of a polyatomic anion acting as a single halide-like unit.

Step 3: {Confirm the identification.}
Because it fits the specific chemical profile of a pseudohalide, $CN^-$ is the correct representative in this list.