The correct answer is (d). Aadhaar is a 12-digit unique identification number issued to all Indian residents based on their biometric and demographic data. It is a voluntary program, but it is required for a number of government services and subsidies. Aadhaar is also used for authentication purposes by banks, telecom companies, and other organizations.
(a) is incorrect because Aadhaar is not a program to help senior citizens. There are other programs that provide assistance to senior citizens, such as the Indira Gandhi National Old Age Pension Scheme.
(b) is incorrect because Aadhaar is not a program to provide nutritional support to adolescent women. There are other programs that provide nutritional support to adolescent women, such as the Mid-Day Meal Scheme.
(c) is incorrect because Aadhaar is not a program to train people for social defense. There are other programs that train people for social defense, such as the National Cadet Corps.