Final answer:
The underlined phrase in the sentence 'Lightning which occurs all over the world is an amazing phenomenon' is non-restrictive.
Step-by-step explanation:
The underlined phrase in the sentence 'Lightning which occurs all over the world is an amazing phenomenon' is non-restrictive.
In this case, the phrase 'which occurs all over the world' adds extra information about 'lightning', but it is not essential to understand the meaning of the sentence.
If we remove the non-restrictive phrase, the sentence still makes sense: 'Lightning is an amazing phenomenon'.
Learn more about Determining whether a phrase or clause is restrictive or non-restrictive