Explanation: The Indian Space Research Organisation (ISRO) is headquartered in Bangalore (Bengaluru), Karnataka. It was established in 1969 under the guidance of Dr. Vikram Sarabhai, who is known as the father of the Indian space program. ISRO is India’s national space agency, responsible for space research, satellite launches, and planetary exploration. It developed major missions such as Chandrayaan (Moon mission), Mangalyaan (Mars Orbiter Mission), and PSLV & GSLV launch vehicles.

Explanation: Windows XP is an operating system (OS) developed by Microsoft. An operating system is system software that manages computer hardware, software resources, and provides services for running application programs. Windows XP, released in 2001, was one of the most popular OS versions used for both personal and business computers. It provides a graphical user interface (GUI), multitasking, and file management capabilities.

Sputnik I was the first artificial satellite to orbit the Earth. It was launched by the Soviet Union on October 4, 1957. The successful launch of Sputnik I marked the beginning of the space age and initiated the space race between the USA and the USSR.

• Explorer I: First U.S. satellite, launched in 1958.
• Vanguard I: A U.S. satellite launched later in 1958.
• Discoverer I: Part of an American reconnaissance satellite program (1959).

Explanation: The longest day in the Southern Hemisphere occurs on 22nd December, which marks the Summer Solstice in that hemisphere. On this date, the South Pole is tilted toward the Sun, resulting in longer daylight hours and shorter nights. Conversely, at the same time, the Northern Hemisphere experiences its winter solstice—the shortest day and longest night of the year. After 22nd December, the days in the Southern Hemisphere gradually begin to shorten.

India’s first successful atomic device was tested at Pokhran in the Thar Desert of Rajasthan on 18th May 1974. The operation was code-named "Smiling Buddha" and was conducted by the Bhabha Atomic Research Centre (BARC) under the leadership of scientists like Dr. Raja Ramanna. This event marked India’s entry into the group of nuclear-capable nations.

Other options (for context)

• Bikaner: A city in Rajasthan, but no nuclear tests were conducted there.
• Barmer: Located near the Pakistan border, not the site of India’s nuclear test.
• Jaisalmer: Close to Pokhran geographically, but not the test location.

Explanation: The rarest blood type in the world is AB⁻ (AB negative). It is found in less than 1% of the global population. People with AB⁻ blood can receive red blood cells from all Rh-negative blood types, but they can donate only to other AB individuals.