Explanation: Penicillin was discovered accidentally by Alexander Fleming in 1928 when he observed that a fungal mold, Penicillium notatum, inhibited the growth of Staphylococcus bacteria in his culture plates. Penicillin became the first antibiotic used to treat bacterial infections and saved millions of lives during World War II. Later, scientists like Howard Florey and Ernst Boris Chain developed methods for its large-scale production.

Explanation: Measles is a highly contagious viral disease caused by the measles virus (a member of the Paramyxovirus group). It spreads through droplets released when an infected person coughs or sneezes. Symptoms include fever, cough, rash, and watery eyes. Other diseases listed — scurvy, asthma, and diabetes — are non-communicable as they do not spread from person to person.

Explanation: A rainbow is formed due to the dispersion of sunlight into its constituent colors and total internal reflection inside water droplets in the atmosphere. The light entering a droplet is refracted, reflected internally, and then refracted again as it exits, producing the beautiful spectrum of colors.

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.

The Green Muffler technique is used to control noise pollution. It involves planting dense rows of trees and shrubs around roads, industrial areas, and public places. The vegetation acts as a natural sound barrier by absorbing, deflecting, and refracting sound waves, thereby reducing the intensity of noise reaching nearby areas. Common plants used for green mufflers include Neem, Ashoka, Ficus, and Cassia.

Other options (for context)

• Air pollution: Controlled by measures like emission filters and afforestation, but not directly by green mufflers.
• Soil pollution: Managed by waste treatment and reduced chemical use, not vegetation barriers.
• Water pollution: Controlled by sewage treatment and reducing industrial discharge, not by plants as mufflers.

Explanation: The DNA sequencing technique was developed by Frederick Sanger in 1977. His method, known as the Sanger chain termination method, determines the nucleotide sequence of DNA using labeled dideoxynucleotides (ddNTPs) that terminate DNA chain elongation. This technique revolutionized molecular biology and became the foundation for genome sequencing projects such as the Human Genome Project.

The purity of milk is tested using a Lactometer. It works on the principle of Archimedes’ principle and is used to measure the specific gravity (density) of milk. Pure milk has a specific gravity ranging between 1.026 and 1.032. If water or other substances are added, the density decreases, indicating adulteration. The lactometer thus helps determine whether the milk is pure or diluted.

Other options (for context)

• Electrometer: Measures electric potential or charge, not related to milk testing.
• Radiometer: Measures radiant energy or light intensity.
• Refractometer: Used to measure refractive index, commonly for sugar solutions, not milk purity.

Explanation: Alternating current (AC) is used for long-distance transmission because energy losses are minimal. The voltage of AC can be easily increased or decreased using transformers, allowing transmission at high voltage and low current, which reduces power loss due to resistance in the wires.