Here are the correct forms for your sentences:

1. The fire was a great **tragedy** that affected the whole town. (tragic)
2. After a long day at work, she enjoys some **relaxation** by the pool. (relax)
3. He has been **unemployed** for several months and is looking for a new job. (employ)
4. She felt very **accomplished** after finishing her first book. (accomplish)
5. The **development** of the new park is exciting for the community. (develop)
6. The new employee is still **inexperienced**, but he is learning quickly. (experience)
7. Winning the championship was a huge **achievement** for the team. (achieve)
8. They traveled through a **mountainous** region with breathtaking views. (mountain)
9. The **depth** of the lake surprised them; it was much deeper than they thought. (deep)
10. They plan to **widen** the road to make it safer for drivers. (width)

1 The fire was a great tragedy that affected the whole town.
2 After a long day at work, she enjoys some relaxation by the pool.
3 He has been unemployed for several months and is looking for a new job.
4 She felt very accomplished after finishing her first book.
The development of the new park is exciting for the community.
The new employee is still inexperienced, but he is learning quickly.
Winning the championship was a huge achievement for the team.
They traveled through a mountainous region with breathtaking views.
The depth of the lake surprised them; it was much deeper than they thought.
They plan to widen the road to make it safer for drivers.