Explanation:

Nucleophiles:
Nucleophiles are species that are attracted to regions of positive charge and are capable of donating a pair of electrons to form a new covalent bond. The strength of a nucleophile can be determined by its ability to donate electrons.

Comparing Nucleophiles:
To compare the nucleophilicity of the given options, we need to consider the factors that influence nucleophilicity. These factors include the charge, size, and polarizability of the nucleophile.

Analysis of Options:
Let's analyze the given options to determine the strongest nucleophile:
- C2H5SH: This is an alkyl thiol, which is a weak nucleophile due to the presence of a relatively large sulfur atom.
- CH3COO-: This is the acetate ion, which is a strong nucleophile. It is negatively charged, small in size, and highly polarizable, making it a potent nucleophile.
- CH3NH2: This is methylamine, which is a moderate nucleophile. It is less nucleophilic than the acetate ion due to the presence of a less electronegative nitrogen atom.
- NC-CH2: This is the cyanide ion, which is a strong nucleophile. It is negatively charged and relatively small, contributing to its nucleophilic strength.

Conclusion:
Among the given options, CH3COO- is the strongest nucleophile due to its negative charge, small size, and high polarizability. It has the ability to readily donate a pair of electrons and form new covalent bonds.