Based on the clues provided, the most likely candidate for metal X is zinc (Zn). Here's why:
Clues and reasoning:
Gas turning limewater milky: This suggests the gas is carbon dioxide (CO2), as it reacts with calcium hydroxide (limewater) to form insoluble calcium carbonate, making the solution cloudy.
Metal X used in galvanization: Zinc is the primary metal used in the galvanization process to protect iron from rust.
Reactions with both HCl and NaOH: Zinc reacts with both dilute hydrochloric acid (HCl) and sodium hydroxide (NaOH) to release hydrogen gas (H2).