The correct answer is 21 June.

• The International Yoga Day has been celebrated annually on 21 June since 2015.
• The theme for International Yoga Day 2021 is 'Yoga for well-being.'
• India, along with United Nations and WHO, is launching an app called M-Yoga aiming to provide easy access to Yogic practice.
• Yoga is an ancient Indian practice that helps in maintaining physical and mental well-being, and over the years.
• On September 27, 2014, during his speech, Prime Minister Narendra Modi put forth his suggestion for the occasion of a Yoga Day.
• 177 member states of UNGA endorsed PM Modi's suggestion to celebrate June 21 as International Yoga Day.
• The first International Day of Yoga was observed around the world on June 21, 2015.
• PM Modi, during his speech at the UNGA, said, "Yoga is an invaluable gift of India's ancient tradition.
• June 21, also called summer solstice, is the longest day of the year.

Previous themes of International Yoga Day :

• 2015: Yoga for Harmony and Peace
• 2016: Yoga for the achievement of the Sustainable Development Goals
• 2017: Yoga for Health
• 2018: Yoga for Peace
• 2019: Yoga for Heart
• 2020: Yoga at Home and Yoga with Family
• 2021: Yoga for well-being.