Identify Common Metals Occurring as Sulfide Ores

To determine which group of metals commonly occurs in nature as sulfide ores, we analyze the principal ores and chemical characteristics of each given element:

1. Hard and Soft Acids and Bases (HSAB) Principle:

   • The sulfide ion ($\text{S}^{2-}$) is large and polarizable, behaving as a soft base.
   • Highly electropositive metals with high charge density, such as $\text{Al}^{3+}$ and $\text{Mg}^{2+}$, are hard acids and strongly prefer hard bases like $\text{O}^{2-}$ (oxides), $\text{CO}_3^{2-}$ (carbonates), or $\text{F}^{-}$ (fluorides). Therefore, $\text{Al}$ and $\text{Mg}$ do not typically occur as sulfides.
   • Less electropositive, more polarizable metal cations like $\text{Ag}^+$, $\text{Cu}^+$, $\text{Cu}^{2+}$, and $\text{Pb}^{2+}$ are soft or borderline acids and have a strong affinity for sulfide ions ($\text{S}^{2-}$), thus readily forming stable sulfide minerals.

2. Common Ores of the Metals:

   • Silver ($\text{Ag}$): Commonly found as argentite or silver glance ($\text{Ag}_2\text{S}$).
   • Copper ($\text{Cu}$): Commonly found as copper pyrites or chalcopyrite ($\text{CuFeS}_2$), copper glance or chalcocite ($\text{Cu}_2\text{S}$), and covellite ($\text{CuS}$).
   • Lead ($\text{Pb}$): Commonly found as galena ($\text{PbS}$).
   • Tin ($\text{Sn}$): Chiefly found as an oxide ore, cassiterite ($\text{SnO}_2$).
   • Magnesium ($\text{Mg}$): Commonly found as carbonates and halides (e.g., magnesite $\text{MgCO}_3$, dolomite $\text{CaCO}_3\cdot\text{MgCO}_3$, carnallite $\text{KCl}\cdot\text{MgCl}_2\cdot 6\text{H}_2\text{O}$).
   • Aluminium ($\text{Al}$): Commonly found as oxide/hydroxide ores (e.g., bauxite $\text{AlO}_x(\text{OH})_{3-2x}$) and fluorides (e.g., cryolite $\text{Na}_3\text{AlF}_6$).

From the above analysis:

• Options containing $\text{Sn}$, $\text{Mg}$, or $\text{Al}$ are incorrect because their common ores are oxides, carbonates, or halides.
• The metals $\text{Ag}$, $\text{Cu}$, and $\text{Pb}$ all commonly occur as sulfide ores ($\text{Ag}_2\text{S}$, $\text{CuFeS}_2/\text{Cu}_2\text{S}$, and $\text{PbS}$).

Therefore, the correct option is (A).