Question

which of the following reagents is nucleophilic?
(A)- Br
(B)- R-OH
(C)- $FeC{{l}_{3}}$
(D)- $C{{O}_{2}}$

Answer 1

. The nucleophilic reagents are electron rich species having a free electron pair or at least a pi bond which reacts at electron deficient sites during a chemical reaction.

Complete step by step answer:
Nucleophiles are nucleus loving species. Since the nucleus of an atom is positively charged, therefore nucleophiles must be electron rich molecules containing at least one lone pair of electrons.
Nucleophiles are Lewis bases as they donate their electron pair in a chemical reaction. There are two types of nucleophiles- negatively charged and neutral nucleophiles.
Negatively charged nucleophiles (anions): $B{{r}^{-}}, {{I}^{-}}, {{F}^{-}}, C{{N}^{-}}, O{{H}^{-}}, R{{O}^{-}}, R{{S}^{-}},etc$
Neutral nucleophiles: ${{H}_{2}}O, N{{H}_{3}}, ROH, RCOOH, RSH, RN{{H}_{2}}, {{R}_{2}}NH, {{R}_{3}}N, etc$

In ROH, an oxygen atom has 2 lone pairs of electrons and it attacks the electron deficient site of a chemical substance during a chemical reaction, hence it is a nucleophile.
Bromine exists as a diatomic molecule and when it gets cleaved it leads to bromide ion which is stable as it acquires noble gas configuration and the other cation formed is unstable and acts as an electrophile.
Carbon dioxide and ferric chloride are also electrophile as the central atom is electron deficient.
So, the correct answer is “Option B”.

Note: We need to keep in mind that nucleophiles are different from that of electrophiles. Electrophiles are electron deficient species which tend to accept electrons, whereas nucleophiles are opposite in nature to that of electrophiles as they are electron rich species and they tend to donate electrons.
Also, alcohols are amphoteric in nature, they can act as base and acid both. Alcohols are weaker acids than water and can react with strong bases and it acts as a weak base in presence of a strong acid.