Explanation: Acids do not turn red litmus to blue; instead, they turn blue litmus paper red. Acids are sour in taste, corrosive in nature, and have a pH value less than 7. Therefore, the statement that acids turn red litmus to blue is incorrect.

Explanation: Edward Jenner, an English physician, is known as the “Father of Immunology.” In 1796, he observed that milkmaids who had previously suffered from cowpox (a mild disease) did not contract smallpox (a deadly viral disease). He tested his hypothesis by injecting a boy with material taken from a cowpox sore and later exposing him to smallpox — the boy did not develop the disease. This led to the development of the first vaccine, derived from the Latin word vacca meaning “cow.”

Significance: Jenner’s discovery laid the foundation of modern immunology and preventive medicine. Smallpox was officially declared eradicated by the WHO in 1980.

Explanation: Bronchitis is an inflammation of the bronchial tubes, which are the air passages of the respiratory tract that carry air to and from the lungs. The condition causes coughing, mucus production, chest discomfort, and difficulty in breathing. It can be caused by viral or bacterial infections, long-term exposure to smoke, dust, or air pollutants. Chronic bronchitis is a serious form often associated with smoking and is part of a group of lung diseases known as COPD (Chronic Obstructive Pulmonary Disease).

Explanation: Producer gas is a mixture of flammable gases such as carbon monoxide (CO) and hydrogen (H₂), along with nonflammable gases like nitrogen (N₂) and carbon dioxide (CO₂). It is produced by the partial combustion of carbon-containing fuels (like coal or coke) with air and steam, and is used as a fuel in industrial furnaces.

Explanation: White blood cells (WBCs), also known as leukocytes, are responsible for producing the immune response in the human body. They defend against infections by attacking bacteria, viruses, and other foreign invaders, helping to maintain the body’s immunity.

Explanation: The phenomenon of radioactivity was discovered by the French physicist Henri Becquerel in 1896. He accidentally discovered that uranium salts emitted invisible rays that could fog photographic plates, even without sunlight. This led to the realization that certain elements spontaneously emit radiations — a property later termed as radioactivity. Subsequently, Marie and Pierre Curie expanded his work and discovered other radioactive elements like polonium and radium.

Explanation: The full form of GPS is Global Positioning System. It is a satellite-based navigation system that provides accurate information about the location, speed, and time anywhere on Earth. Developed by the U.S. Department of Defense, GPS uses a network of at least 24 satellites orbiting the Earth. It is widely used in navigation, mapping, military operations, aviation, and smartphone tracking applications.