The correct answer is option 'A', which is 5th June. World Environment Day is celebrated on this day every year.

World Environment Day:
- World Environment Day is observed annually on 5th June to raise awareness about environmental issues and encourage people to take action to protect the environment.
- It was established by the United Nations General Assembly in 1972 on the first day of the United Nations Conference on the Human Environment in Stockholm, Sweden.
- The main objective of World Environment Day is to promote positive environmental action at an individual, community, and global level.
- Each year, World Environment Day has a different theme that focuses on a specific environmental issue. The theme for 2021 is "Ecosystem Restoration."
- The United Nations Environment Programme (UNEP) coordinates the global celebrations of World Environment Day, which includes various activities such as clean-up campaigns, tree planting, awareness workshops, seminars, and conferences.

Importance of World Environment Day:
- World Environment Day plays a crucial role in raising awareness about environmental challenges and mobilizing individuals and communities to take action.
- It provides an opportunity for governments, organizations, and individuals to showcase their environmental initiatives and projects.
- The day also serves as a platform for discussing and addressing pressing environmental issues such as climate change, pollution, deforestation, and loss of biodiversity.
- World Environment Day encourages people to adopt more sustainable practices in their daily lives, such as reducing waste, conserving energy, using eco-friendly products, and promoting biodiversity conservation.

Impact of World Environment Day:
- World Environment Day has had a significant impact in creating global awareness and mobilizing action towards environmental conservation.
- It has helped in raising public consciousness about environmental issues and influencing policy decisions at national and international levels.
- The day has contributed to the establishment of various environmental laws, regulations, and initiatives aimed at protecting and preserving the environment.
- World Environment Day has also inspired numerous environmental campaigns and movements, promoting sustainable development and environmental justice.

Conclusion:
World Environment Day, celebrated on 5th June each year, is a global event that raises awareness about environmental issues and encourages individuals and communities to take action. It plays a crucial role in mobilizing efforts towards environmental conservation and sustainability.