Amphoteric hydroxides dissolve in excess NaOH

Steps:

• Precipitates form in both experiments upon initial NaOH addition, indicating metal hydroxides.
• Excess NaOH tests for amphoteric behavior, where certain hydroxides (e.g., Al(OH)3, Zn(OH)2) react to form soluble complexes.
• In experiment 1, the precipitate dissolves due to amphoteric nature, confirmed by observation.
• In experiment 2, the same dissolution occurs, matching the x symbol for dissolution in both.

Why C is correct:

• Amphoteric hydroxides dissolve in excess base per the reaction Al(OH)3 + OH- → [Al(OH)4]-, forming soluble tetrahydroxoaluminate.

Why the others are wrong:

• A incorrectly states precipitates remain in both, ignoring amphoteric dissolution.
• B mislabels outcomes as remaining without dissolution in either.
• D duplicates C's description but uses incorrect formatting or symbols for the experiments.

Final answer: C