Explanation:

In school, students are required to wear a uniform. The uniform is a specific set of clothing that is designated by the school administration. It is important for students to wear a uniform in school for several reasons.

Uniform:
- Wearing a uniform helps to create a sense of unity and belonging among students. When everyone is dressed in the same attire, it eliminates any discrimination or judgment based on clothing choices.
- Uniforms also promote a sense of discipline and professionalism. By wearing a uniform, students learn to follow rules and regulations, which prepares them for future situations where dress codes may be required.
- Additionally, uniforms help to create a safe and secure environment. It becomes easier to identify who belongs to the school community and who doesn't, preventing unauthorized individuals from entering the premises.
- Uniforms also save time and effort in choosing what to wear each day. It eliminates the need for students to spend time picking out outfits, allowing them to focus on more important tasks like studying and learning.

Other options:
- Party dress: Party dresses are typically worn for special occasions or celebrations and are not suitable for everyday school attire.
- Night suit: Night suits are sleepwear and are not appropriate for school settings.
- Raincoat: Raincoats are worn to protect oneself from rain and are not part of a school uniform.

In conclusion, the correct answer is option 'C' - Uniform. Wearing a uniform in school promotes unity, discipline, professionalism, safety, and saves time and effort in choosing daily outfits.