Consider the following compounds: I. BF3 II. IF7 III. CO2 IV. PCl5 Among these…

Concept: An electrophile ("electron-pair lover") is an electron-deficient species that seeks to accept a pair of electrons from a nucleophile — equivalently, a Lewis acid. A central atom is genuinely electron-deficient when it either has an incomplete octet, or carries a significant partial positive charge from strong bond polarization. A central atom that has already achieved a complete octet — even an expanded one, with more than eight electrons around it — is not electron-deficient in this sense, so it is not typically classed as an electrophile, even though it may still be capable of further coordination under special conditions.

1. BF3: boron has only six electrons around it, an incomplete octet, so it is a genuine electrophile.

2. IF7: iodine already has an expanded octet (fourteen electrons, from seven bond pairs); having already accommodated more than a full octet, it is not electron-deficient and is not typically classed as an electrophile.

3. CO2: the two C=O bonds pull electron density from carbon toward the more electronegative oxygens, leaving carbon with a significant partial positive charge that nucleophiles such as OH- attack, so it is a genuine electrophile through bond polarization.

4. PCl5: phosphorus already has an expanded octet (ten electrons, from five bond pairs); like IF7, it has already accommodated more than a full octet and is not typically classed as an electrophile.

Cross-check: the two electrophiles here, BF3 and CO2, are the species whose central atom is genuinely short of electron density — through an incomplete octet or through strong bond polarization. IF7 and PCl5 already have more than a full octet around their central atom; already having extra electron pairs accommodated is the opposite of electron deficiency, so grouping them with BF3 and CO2 would conflate octet expansion with octet deficiency, two distinct phenomena.

Hence only BF3 and CO2 — I and III — are electrophiles.