Define nucleophilic substitution and elimination reactions in the context of halogenoalkanes. What is the key difference between these two mechanisms?

Nucleophilic substitution involves the replacement of a halogen atom in a halogenoalkane with a nucleophile, while elimination involves the removal of a halogen and a hydrogen atom, resulting in the formation of a double bond. The key difference is that substitution results in a single product, whereas elimination produces an alkene as a product. Nucleophilic substitution typically occurs under conditions favoring lower temperatures and polar solvents, while elimination is favored at higher temperatures and in less polar solvents.

This question tests the student's understanding of two fundamental organic reaction mechanisms involving halogenoalkanes. By defining both processes and identifying their key difference, students demonstrate their grasp of reaction conditions and product formation.