Name the non-metals which show the following properties :
(i) A non-metal which has lustre and is a good conductor of electricity.
(ii) A non-metal which is the hardest natural substance.
(iii) A non-metal which is essential for respiration
(iv) A non-metal which is the source of energy in the sun and stars.

Explanation

### Step-by-Step Solution:

1. **Identify the first property**: The question asks for a non-metal that has lustre and is a good conductor of electricity.

**Answer**: The non-metal that fits this description is **Graphite**. Graphite is an allotrope of carbon that has a shiny appearance (lustre) and can conduct electricity due to the presence of free electrons in its layered structure.

2. **Identify the second property**: The next property is to find a non-metal that is the hardest natural substance.

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