An electrophilic reagent is

CONCEPT:

Electrophilic Reagent

• An electrophilic reagent, also known as an electrophile, is a species that seeks out electrons to form a chemical bond.
• Electrophiles are electron-deficient species, meaning they have a positive charge or a partial positive charge, or they are neutral species with an incomplete octet.

EXPLANATION:

• Electrophiles are attracted to electron-rich regions in a molecule, where they can accept an electron pair to form a new covalent bond.

• Electron deficient species - This is correct because electrophiles are indeed electron-deficient and seek additional electrons.
• Electron rich species - This is incorrect because electron-rich species are nucleophiles, not electrophiles.
• Negatively charged species - This is incorrect because negatively charged species are typically nucleophiles.

​Therefore, the correct answer is option 1: Electron deficient species.