Amphoteric oxide of Period 3 element

Steps:

• Period 3 elements form oxides; Y is solid and reacts with hot NaOH to place X in anion, showing acidic/amphoteric nature.
• Y also reacts with hot conc. HCl to place X in anion, showing basic/amphoteric nature.
• Thus, Y is amphoteric; in Period 3, only Al₂O₃ fits (Al in group 13).
• Al has outer configuration 3s² 3p¹, so 1 p electron.

Why B is correct:

• Al (3p¹) forms Al₂O₃, which reacts with NaOH to [Al(OH)₄]⁻ and with conc. HCl to [AlCl₄]⁻, placing Al in anions per amphoteric definition.

Why the others are wrong:

• A (0): Mg (group 2, 3s²) forms basic MgO; reacts with HCl to MgCl₂ (Mg²⁺ cation), not anion; inert with NaOH.
• C (2): Si (group 14, 3s² 3p²) forms acidic SiO₂; reacts with NaOH to [SiO₃]²⁻ but insoluble in HCl, no Cl-anion.
• D (3): P (group 15, 3s² 3p³) forms acidic P₄O₁₀; reacts with NaOH to [PO₄]³⁻ but with HCl yields H₃PO₄, no stable P-Cl anion.

Final answer: B