Edward Jenner, an English physician, is credited with developing the first successful vaccine in 1796. He discovered that milkmaids who had contracted cowpox were immune to smallpox, a deadly disease at the time. Jenner tested his theory by inoculating a young boy with material from cowpox lesions and later exposing him to smallpox. The boy did not develop the disease, proving immunity. This discovery laid the foundation for immunology and modern vaccination. It led to the eventual eradication of smallpox worldwide. Other options are incorrect as they do not match the historical timeline. Thus, 1796 is the correct answer, marking a major breakthrough in medical science and public health.

The Uch Gas Field is located in Balochistan, Pakistan, and is an important source of natural gas for the country. It was discovered in the mid-20th century and has been developed primarily to supply fuel for power generation. Natural gas from Uch is used in thermal power plants, helping to generate electricity and support industrial activities. This contributes significantly to Pakistan’s energy sector and reduces reliance on imported fuels. Balochistan is rich in natural resources, including gas, coal, and minerals. Other provinces like Sindh also have major gas fields, such as Qadirpur, but Uch specifically belongs to Balochistan. Khyber Pakhtunkhwa and Punjab are not known for the Uch gas field. Therefore, Balochistan is the correct answer. Knowledge of such resources is important for understanding national energy infrastructure and economic geography.

Sunspots are dark regions that appear on the surface of the Sun due to intense magnetic activity that lowers the surface temperature in those areas. The first recorded telescopic observation of sunspots is credited to Thomas Harriot, an English astronomer, in 1610. He used an early telescope to observe the Sun and documented these spots before Galileo’s more widely known observations. This discovery challenged the long-standing Aristotelian belief that celestial bodies were perfect and unchanging. The presence of spots on the Sun suggested that it was dynamic and imperfect. Later astronomers such as Galileo Galilei and Christoph Scheiner studied sunspots more extensively and tracked their movement, which helped establish that the Sun rotates on its axis. Albert Einstein is known for the theory of relativity, Isaac Newton for gravity and laws of motion, and René Descartes for contributions to philosophy and mathematics. None of them observed sunspots first. Thus, Thomas Harriot is considered the earliest observer, making option D correct. His work contributed significantly to the development of modern astronomy and our understanding of solar activity.

Balochistan became a province in 1970 after administrative reforms. Thus correct is 1970.

The Rio Earth Summit was held in June 1992 in Brazil and focused on sustainable development and environmental protection.