Here are the corrections for each sentence based on the mistakes in the underlined parts:

1. **Original**: I love the **spicy food** in this city. The **hottest** the food is, the **more** I like it.
**Correction**: Change "hottest" to "hotter."
**Corrected**: The **hotter** the food is, the **more** I like it.

2. **Original**: I got stuck in a traffic jam yesterday. The **more congested** the road was, the **tired** I became.
**Correction**: Change "tired" to "more tired."
**Corrected**: The **more congested** the road was, the **more tired** I became.

3. **Original**: The **modern** the library is, the **more attractive** it is to teenagers.
**Correction**: Change "modern" to "more modern."
**Corrected**: The **more modern** the library is, the **more attractive** it is to teenagers.

4. **Original**: The streets are getting dirtier. The **more crowded** this city is, **more polluted** it becomes.
**Correction**: Change "more polluted" to "the more polluted."
**Corrected**: The **more crowded** this city is, **the more polluted** it becomes.

5. **Original**: The **denser** the buildings are, the **more ugly** the city becomes. It’ll soon look like a concrete jungle.
**Correction**: Change "more ugly" to "uglier."
**Corrected**: The **denser** the buildings are, the **uglier** the city becomes.

Here are the complete corrected sentences:
1. I love the spicy food in this city. The hotter the food is, the more I like it.
2. I got stuck in a traffic jam yesterday. The more congested the road was, the more tired I became.
3. The more modern the library is, the more attractive it is to teenagers.
4. The streets are getting dirtier. The more crowded this city is, the more polluted it becomes.
5. The denser the buildings are, the uglier the city becomes. It’ll soon look like a concrete jungle.