Question

which substance is used in fertilizers?
slaked lime ($\text{ca(oh}_2\text{)})
formic acid ($\text{hcooh}$)
nitric acid ($\text{hno}_3$)
lithium hydroxide ($\text{lioh}$)

Explanation:

Fertilizers require key nutrients like nitrogen, phosphorus, or potassium. Nitric acid ($\text{HNO}_3$) is a source of nitrogen, and it is used to produce nitrogen-based fertilizers. Slaked lime is used in soil pH adjustment but not as a fertilizer core nutrient source; formic acid is primarily used in preservatives or textiles; lithium hydroxide is used in batteries and air purification, not fertilizers.

Answer:

nitric acid ($\text{HNO}_3$)