Explanation: Acid rain is caused by the presence of sulphur dioxide (SO₂) and nitrogen oxides (NOₓ) in the atmosphere. These gases are mainly released from the burning of coal, petroleum, and other fossil fuels in industries and vehicles. When they combine with water vapor and oxygen in the air, they form sulphuric acid (H₂SO₄) and nitric acid (HNO₃). These acids mix with rainwater and fall as acid rain, which damages soil, crops, aquatic life, and even monuments like the Taj Mahal.

Explanation: The full form of OMR is Optical Mark Recognition. It is a technology used to detect marks made on specially designed paper forms, such as answer sheets in competitive exams or surveys. Candidates mark their answers by filling bubbles with dark ink or pencil, and the OMR scanner reads these marks by detecting reflected light. This process allows for fast, accurate, and automated data collection without manual checking, minimizing human errors and saving time.

Explanation: A parity bit is added to binary data in a computer system for error detection. It helps identify whether data has been altered during transmission or storage. The parity bit makes the total number of 1s either even (even parity) or odd (odd parity), allowing simple error checking.

Explanation: Vitamins are classified into two categories based on their solubility — fat-soluble and water-soluble. Vitamin C (ascorbic acid) and the B-complex vitamins are water-soluble, meaning they dissolve in water and are not stored in the body. Therefore, they must be consumed regularly through diet. Deficiency of Vitamin C causes scurvy, characterized by bleeding gums and delayed wound healing.

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: Organic farming is an agricultural method that emphasizes the use of natural inputs and eco-friendly techniques. It avoids chemical fertilizers, pesticides, and genetically modified organisms (GMOs). Instead, it uses organic manures (compost, green manure, and farmyard manure), crop rotation, and biological pest control to maintain soil health and productivity. Chemical fertilizers are excluded because they degrade soil quality and harm beneficial soil organisms over time.

Explanation: Nuclear fission is the process in which the nucleus of a heavy atom, such as Uranium-235 or Plutonium-239, splits into two or more lighter nuclei when bombarded by a slow-moving neutron. This reaction releases a large amount of energy, along with additional neutrons that can trigger further fission reactions—leading to a chain reaction. This principle is used in nuclear reactors for power generation and in atomic bombs for explosive energy release.

Explanation: The heart is enclosed in a double-layered protective membrane called the pericardium. The outer fibrous layer protects the heart and anchors it within the chest cavity, while the inner serous layer secretes pericardial fluid that reduces friction during heartbeats. This fluid-filled sac ensures smooth and cushioned movement of the heart as it contracts and relaxes continuously.