Final answer:
Among the given options, NH3 (ammonia) is an example of a Lewis base because it can donate a pair of electrons to form a coordinate covalent bond.
Step-by-step explanation:
The question asks to identify an example of a Lewis base among the given options. A Lewis baseis defined as a species that donates an electron pair. The correct choice here is NH3 (ammonia), as it has a lone pair of electrons that can be donated to form a coordinate covalent bond. Therefore, NH3 is the Lewis base among the options provided.