The hardest substance present in a tooth is

Options

A. crown
B. enamel
C. dentine
D. cement

Explanation

To determine the hardest substance present in a tooth, we need to analyze the options provided:

1. **Crown**: This is the part of the tooth that is visible above the gum line. While it is an important part of the tooth, it is not a substance itself.

2. **Enamel**: This is the outermost layer of the tooth and is known to be the hardest substance in the human body. It is shiny and white, providing protection to the underlying layers of the tooth.

3. **Dentine**: This is the tissue located beneath the enamel. While it is also a hard tissue, it is not as hard as enamel.

4. **Cementum**: This is a hard substance that covers the roots of the teeth. It is important for anchoring the tooth in the jawbone but is not as hard as enamel.

After analyzing these options, we conclude that the hardest substance present in a tooth is **enamel**.

### Step-by-Step Solution:
1. Identify the components of a tooth: Crown, enamel, dentine, and cementum.
2. Define each component:
- Crown: The visible part of the tooth.
- Enamel: The outer layer, known for its hardness.
- Dentine: The layer beneath enamel, less hard than enamel.
- Cementum: Covers the roots of the tooth, also less hard than enamel.
3. Compare the hardness of each component.
4. Conclude that enamel is the hardest substance in a tooth.