The World Population Day is observed on

Oct-04
May-31
Jul-11
Dec-10

The correct answer is (a). World Population Day is observed on July 11 every year. It was established by the United Nations in 1989 to raise awareness of global population issues. The day marks the day in 1987 when the world’s population reached 5 billion.

Option (b) is incorrect because May 31 is not World Population Day. It is the International Day of Peace.

Option (c) is incorrect because July 11 is not World Population Day. It is the International Day of Sport for Development and Peace.

Option (d) is incorrect because December 10 is not World Population Day. It is Human Rights Day.