To determine which substance is used in fertilizers among the given options, let's examine each of them:
1. Slaked lime (Ca(OH)_2):
- Slaked lime is primarily used to reduce soil acidity. It is commonly used in agriculture to improve soil quality but is not typically considered a primary ingredient in fertilizers to provide nutrients.
2. Formic acid (HCOOH):
- Formic acid is primarily used in silage preservation and other industrial applications. It is not commonly used in fertilizers.
3. Nitric acid (HNO_3):
- Nitric acid is a significant component in the production of ammonium nitrate, which is a common nitrogen-based fertilizer. Nitrogen is a crucial nutrient that promotes plant growth. Therefore, nitric acid is often used in the fertilizer industry.
4. Lithium hydroxide (LiOH):
- Lithium hydroxide is mainly used in battery production and other industrial applications but not in fertilizers.
After evaluating the uses of each substance, we conclude that among the given options, nitric acid (HNO_3) is the substance used in fertilizers.
Thus, the correct answer is option 3:
Nitric acid (HNO_3) is used in fertilizers.
