Shanghai is a city in China.

. An element is an essential or characteristic part of something abstract. For example, "the death had all the elements of a great tabloid story" A city is not a part of something abstract, therefore, you cannot say, "Shanghai is an element in China". You can say, "Shanghai is a city in China". I hope this helps, if you need conversation practice, I am willing to plan unique lessons to help you improve your skills. Regards.