A form of which of the following non-metals is the hardest substance ?

Options

A. Phosphorus
B. Sulphur
C. Iodine
D. Carbon

Explanation

### Step-by-Step Solution:

1. **Identify the Question**: The question asks for the hardest substance among non-metals.

2. **List the Non-Metals**: Common non-metals include carbon, sulfur, phosphorus, and nitrogen.

3. **Understand Allotropes**: Allotropes are different forms of the same element. For example, carbon has several allotropes, including graphite and diamond.

4. **Determine Hardness**: Among the allotropes of carbon, diamond is known to be the hardest natural substance.

5. **Conclude the Answer**: Since diamond is an allotrope of carbon and is the hardest substance, the answer to the question is carbon.

6. **Select the Option**: If given options, choose the one that corresponds to carbon.

### Final Answer:
The hardest substance among non-metals is **carbon**, specifically in the form of **diamond**.

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