The lightest city the word(a)xhengxen(b)Ecuador(c)hongkong

This question appears to be a riddle or a trick question, as "lightest city" is not a standard geographical or scientific classification. Common riddle answers for "the lightest city" are "Light-ning" or "Light-house," neither of which is a city.

Among the given options:

• (a) Zhengzhou is a city in China.
• (b) Ecuador is a country, not a city.
• (c) Hong Kong is a city (a Special Administrative Region of China).

Since Ecuador is a country and not a city, it cannot be "the lightest city." Between Zhengzhou and Hong Kong, there is no known characteristic that would make one definitively "lighter" than the other in any conventional sense.

Given the nature of the question, it's likely a play on words, but without further context or a clear pun related to the city names, it's impossible to determine a "lightest city" based on conventional definitions. However, if the question is a trick, then (b) Ecuador is the only option that is not a city, making it distinct from the others.