Bhawesh...i think they give a incorrect option to u...but actually the correct option is 4 only....(CH3)3CO^-..because in this case 3 electron donating to -CH3 group that mean tends to increase the electron density of oxygen (O) atom..so the correct option is 4 only...hope u clear....!!

Introduction
When determining the most reactive nucleophile among the given options, we must consider factors such as charge, electronegativity, steric hindrance, and resonance effects.
Nucleophile Options
- (1) CH3O^- (Methoxide Ion)
- (2) C6H5O^- (Phenoxide Ion)
- (3) (CH3)3CHO^- (Tert-Butoxide Ion)
- (4) (CH3)3CO^- (Tert-Butyl Anion)
Analysis of Each Nucleophile
- CH3O^- (Methoxide Ion)
- Strong nucleophile due to the negative charge on oxygen.
- Less steric hindrance allows for easier attack on electrophiles.
- C6H5O^- (Phenoxide Ion)
- The negative charge is delocalized over the aromatic system, reducing nucleophilicity.
- Resonance stabilization makes it less reactive compared to methoxide.
- (CH3)3CHO^- (Tert-Butoxide Ion)
- Sterically hindered due to three bulky methyl groups.
- While it has a negative charge, steric hindrance reduces its nucleophilic ability.
- (CH3)3CO^- (Tert-Butyl Anion)
- Also sterically hindered with bulky groups; however, it is not a typical nucleophile in reactions.
- Its negative charge is less effective in nucleophilic attacks.
Conclusion
The most reactive nucleophile among the options is CH3O^- (Methoxide Ion). It has a strong negative charge, low steric hindrance, and no resonance stabilization to decrease its reactivity. Thus, it is well-suited for nucleophilic attacks compared to the other options.