Question

Which of the following is electrophilic reagent?

A.${ H }_{ 2 }{ O }$
B.${ NH }_{ 3 }$
C.${ OH }^{ - }$
D.${ NO }_{ 2 }^{ + }$

Answer 1

Hint: An electrophile (or electrophilic reagent) is a reagent that forms a bond to its reaction partner (the nucleophile) by accepting both bonding electrons from that reaction partner. It is electron deficient.

Complete answer:
An Electrophile is a chemical species that is electron-deficient. It will seek out an electron-rich site in an organic molecule.
A.${ H }_{ 2 }{ O }$ = Water can act as both an electrophile and nucleophile but water seems to be a stronger nucleophile than an electrophile as oxygen has two lone pairs so it will donate an electron pair to the electron-deficient center, hence a better nucleophile.
B.${ NH }_{ 3 }$ = Ammonia is a nucleophile as N has a lone pair of electrons and a partial negative charge on the N-atom, so it can act as a Lewis base. Hence, ammonia is a nucleophile.
C.${ OH }^{ - }$ = It is a nucleophile because of the presence of lone pairs of electrons on O which increases electron density on atoms.
D.${ NO }_{ 2 }^{ + }$ = The central atom is N, which has ${ 5 }$ electrons in its valence shell. There is a +ve charge on the molecule, which tells us that it is an electron-deficient molecule. It can accept electron pairs from electron-rich species to form complexes. So it behaves like an electrophile.
Hence, the correct option is D.

Additional Information:
Nucleophiles can act as Lewis bases whereas electrophiles can act as Lewis acid.
Nucleophiles can undergo nucleophilic substitution and addition reactions while electrophiles can undergo electrophilic addition and substitution reaction.

Note: The possibility to make a mistake is that you may choose option A. Water is an electrophile but it is a stronger nucleophile as it has a lone pair of electrons, so the density of electrons will increase.