Generally, Group 15 elements in 3 oxidation state form binary compounds with metals of type \(M_3X_2\) (X = N, P, As, Sb, Bi). Which of the following elements may not have an ore with formula \(M_3X_2\)?

(A) N

(B) P

(C) As

(D) Sb

(E) Bi

Choose the correct answer from the options given below:

(C) only

The correct answer is option 2. (C) only.

Let us dive deeper into why Arsenic (As) is identified as the element that may not have an ore with the formula \(M_3X_2\).

Group 15 Elements and Their Binary Compounds:

Group 15 elements (N, P, As, Sb, Bi) typically form binary compounds with metals in which they exhibit a -3 oxidation state. The general formula for such compounds is \(M_3X_2\), where \(M\) is a metal and \(X\) is the Group 15 element.

Key Points for Each Element:

A. Nitrogen (N):

Nitrogen forms nitrides like \(M_3N_2\) (e.g., aluminum nitride, \(AlN\)). Nitrides are stable and commonly found in nature, often as part of ores.

B.Phosphorus (P):

Phosphorus forms phosphides like \(M_3P_2\) (e.g., calcium phosphide, \(Ca_3P_2\)). Phosphides are stable and occur naturally, often in the form of mineral ores.

C. Arsenic (As):

Arsenic can form arsenides (\(M_3As_2\)) with metals, but these are less common and less stable compared to nitrides and phosphides. Arsenic has a strong tendency to form covalent compounds rather than ionic ones. It frequently occurs in ores as sulfides (like arsenopyrite, \(FeAsS\)) rather than arsenides. This unique chemistry of arsenic makes the formation of stable \(M_3As_2\) ores less likely.

D. Antimony (Sb):

Antimony forms antimonides (\(M_3Sb_2\)), which are more common and stable than arsenides, though still less so than nitrides and phosphides.

E. Bismuth (Bi):

Bismuth forms bismuthides (\(M_3Bi_2\)), but these are rare. Bismuth typically occurs in ores as sulfides or oxides rather than as bismuthides.

Why Arsenic (As) May Not Have an Ore with Formula \(M_3X_2\):

Stability and Occurrence:

Arsenic's tendency to form covalent bonds and occur in ores as sulfides or oxides (rather than arsenides) makes it less likely to form a stable ore with the formula \(M_3As_2\). Arsenic compounds with the formula \(M_3X_2\) are not commonly found in nature, especially when compared to the corresponding nitrides, phosphides, antimonides, or bismuthides.

Chemical Properties:

Arsenic exhibits a lower tendency to form binary ionic compounds with metals in the +3 oxidation state, leading to the relative scarcity of arsenide ores with the specific \(M_3X_2\) formula.

Conclusion:

Arsenic (As) is less likely to have an ore with the formula \(M_3X_2\) due to its chemical properties and tendency to form different types of compounds (such as covalent arsenides or sulfides). This is why the correct answer is option 2: (C) only, meaning arsenic may not have an ore with the formula \(M_3X_2\).