Aluminum's acidity and amphoteric hydroxide

Steps:

• AlCl3 in water hydrolyzes: Al^{3+} + H2O ⇌ Al(OH)^{2+} + H^+, lowering pH below 7, so statement 1 is correct.
• Precipitation requires Al^{3+} + 3OH^- → Al(OH)3(s), needing y = 3x mol NaOH, so y ≠ x and statement 2 is false.
• Excess NaOH dissolves the precipitate: Al(OH)3(s) + OH^- → [Al(OH)4]^-, retaining x mol aluminum in solution Z, so statement 3 is correct.

Why D is correct:

• D identifies statements 1 and 3 as true, based on Al^{3+} acidity and amphoteric nature of Al(OH)3.

Why the others are wrong:

• A includes only 1, omitting 3.
• B includes only 2, which is false.
• C includes 1 and 2, but 2 is false.

Final answer: D