Which of the following species can act as the strongest base?
The answer is the option (ii). The strength of a base is determined by the corresponding conjugate acid. If the acid is weak, the base is strong.
In the mentioned options, the phenol having a benzene ring has higher acidity than aliphatic alcohols. Since the acidity of water is more than alcohol, it makes the least acidic product. Since, according to the above-mentioned point, the weaker acid makes a strong base. will be the strongest base in all four options. This makes option (ii) as is the right answer.