World Environment Day is observed every year on:

The correct answer is 5 June. World Environment Day is celebrated annually on June 5th, as designated by the United Nations General Assembly in 1972 to raise global awareness and encourage action for the protection of the environment.

Significance of 5 June

• Historical Origin: The date marks the opening day of the Stockholm Conference on the Human Environment (1972), the first major international conference on environmental issues. The UN established World Environment Day later that same year.
• Annual Themes and Hosts: Each year, a different country hosts the official celebrations, and a theme is chosen to focus global efforts — past themes include "Beat Plastic Pollution," "Ecosystem Restoration," and "Only One Earth."
• Global Observance: It is now celebrated in over 143 countries, involving governments, businesses, and citizens in activities like tree planting, clean‑up campaigns, and policy pledges.
• Why Other Dates Are Incorrect: 1 May is International Workers' Day; 14 August is Pakistan's Independence Day; 22 April is Earth Day — a separate environmental observance that predates World Environment Day.

Thus, World Environment Day is observed on 5 June every year.