Giant metallic elements with acidic chloride solutions

Steps:

• Elements with giant structures include metals like aluminium and magnesium (giant metallic lattices) and silicon (giant covalent); phosphorus has simple molecular structure.
• Eliminate C and D as they include phosphorus, lacking giant structure.
• Silicon chloride (SiCl4) reacts violently with water to form HCl gas and insoluble silica, not a clear solution.
• Aluminium chloride (AlCl3) and magnesium chloride (MgCl2) dissolve to form solutions where metal cations hydrolyze, releasing H+ for pH <5.

Why B is correct:

• Both aluminium and magnesium have giant metallic structures; their chlorides hydrolyze via Al(H2O)6^3+ ⇌ Al(H2O)5OH^2+ + H+ and similar for Mg^2+, producing acidic solutions (pH <5) due to high charge density polarizing water.

Why the others are wrong:

• A: Silicon's SiCl4 forms a precipitate and gas, not a homogeneous acidic solution.
• C: Phosphorus lacks giant structure.
• D: Phosphorus lacks giant structure.

Final answer: B