Concept:The United Nations designated 21st June as the International Day of Yoga.Explanation:21st June was officially proclaimed by the United Nations as the International Day of Yoga, first celebrated in 2015.This date marks the summer solstice, which is considered an ideal period for meditation in yogic traditions.The other options do not correspond to 21st June: International Mother Language Day is on 21st February, International Widow’s Day on 23rd June, and International Day against Drug Abuse on 26th June.Answer:International Day of Yoga