Fill in the following black with suitable words :
Tooth decay happens when the bacteria present in mouth turn the sugar present in our food into ______.

Answer

Tooth decay happens when the bacteria present in the mouth turn the sugar present in our food into **acid**.

### Step-by-Step Solution:

1. **Understanding Tooth Decay**: Tooth decay, also known as dental caries, is a process that occurs in the mouth when certain conditions are met.

2. **Role of Bacteria**: The mouth contains various types of bacteria. Some of these bacteria are beneficial, while others can be harmful and contribute to tooth decay.

3. **Sugar in Food**: When we consume foods that contain sugar, such as sweets, bread, and cereals, these sugars can stick to our teeth.

4. **Bacterial Action**: The harmful bacteria present in the mouth feed on the sugars from the food we eat.

5. **Production of Acid**: As the bacteria metabolize the sugar, they produce acid as a byproduct. This acid is what leads to the decay of tooth enamel.

6. **Consequences of Acid**: The acid produced can erode the enamel, which is the hard outer layer of our teeth, leading to holes or cavities.

7. **Final Answer**: Therefore, the blank can be filled with the word **acid**.