Question

which compound plays an important role in leather processing and electroplating?
○ nitric acid
○ hydrochloric acid
○ ammonia
○ magnesium hydroxide

Explanation:

• Nitric acid ($\ce{HNO_3}$) is mainly used in making fertilizers, explosives, etc., not for leather processing or electroplating.
• Hydrochloric acid ($\ce{HCl}$) is used in cleaning, pickling metals, but not prominently in leather processing and electroplating as ammonia is.
• Ammonia ($\ce{NH_3}$) is used in leather processing (e.g., in tanning to adjust pH, soften leather) and electroplating (to control pH, act as a complexing agent for metal ions).
• Magnesium hydroxide ($\ce{Mg(OH)_2}$) is a base used in antacids, water treatment, not in leather processing or electroplating.

Answer:

ammonia