Here are the corrections for mistakes in the provided sentences:

5. Some snakes have hollow teeth **that** they are called fangs that they use to poison their victim.
- Correction: "that" replaces "they."

6. The nitrogen makes up over 78 percent of the Earth’s atmosphere, the gaseous mass surrounding the planet.
- Correction: Add a period instead of a comma after "atmosphere."

7. Why so many students are weak at reading and math **is a question** that continues to disturb educators.
- Correction: "is a question" should be rephrased to remove confusion.

8. Although apples do not grow during the cold season, apple trees must have **such a** season to flourish.
- Correction: "such season" should be "such a season."

9. Dentistry is a branch of medicine that developed very dramatically in the last twenty years.
- No correction needed.

10. Rabbits have large front **teeth**, short tails, and hind legs’ feet adapted for running and jumping.
- Correction: "tooth" should be "teeth."

These adjustments enhance clarity and grammatical accuracy in the sentences.