The substance W is a folssil fuel . It occurs deep below the ground in certain areas of the earth. Another fossil fuel X is found trapped above the deposits of W. When W is subjected to a process called Y, then a number of different products are collected at different temperature ranges which are put to different uses. A special grade of product Z obtained in this way is used as aviation fuel in jet aeroplanes.
a) What are i) W and ii) X ?

Explanation

To solve the question, we need to identify the substances W and X based on the clues provided. Let's break it down step by step.

### Step 1: Identify Substance W
- The question states that substance W is a fossil fuel that occurs deep below the ground.
- The most common fossil fuel found deep underground is petroleum (crude oil).

### Step 2: Identify Substance X
- The question mentions that another fossil fuel, X, is found trapped above the deposits of W.
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