Q90. Who first stated the zeroth law of thermodynamics explicitly in the twentieth century?
[RRB NTPC Undergraduate – 2025]
(A) Hugh L. Callendar
(B) James P. Espy
(C) Rudolf Clausius
(D) Ralph H. Fowler
Answer: (D) Ralph H. Fowler
Explanation: Ralph H. Fowler is associated with formulating and naming the zeroth law in the 1930s. The law says that systems individually in thermal equilibrium with a third system are in equilibrium with each other, providing a foundation for temperature measurement.
Q89. What was Gregor Mendel’s most important contribution to genetics?
[RRB Group D – 2025]
(A) Theory of evolution
(B) Discovery of the DNA structure
(C) Inheritance of acquired characteristics
(D) Laws of inheritance
Answer: (D) Laws of inheritance
Explanation: Through pea-plant breeding experiments, Gregor Mendel identified regular patterns in how traits pass between generations. His principles of segregation and independent assortment became central to classical genetics, although the molecular basis of genes was discovered much later.
Q88. Who discovered the laws governing levers and investigated the principles of pulleys?
[SSC CGL Tier-II (2024 cycle) – 2025]
(A) Archimedes
(B) Pythagoras
(C) Eudoxus
(D) Democritus
Answer: (A) Archimedes
Explanation: Archimedes analysed equilibrium in levers and formulated the principle that turning effects depend on force and distance from a fulcrum. His work on simple machines established mechanical ideas still used in engineering, lifting equipment and physics instruction.
Q87. What was the name of the instrument for measuring wind speed that dates back to the fifteenth century?
[SSC CGL – 2024]
(A) Transmissometer
(B) Dropsonde
(C) Anemometer
(D) Ceiling projector
Answer: (C) Anemometer
Explanation: An anemometer measures wind speed. Early descriptions of wind-measuring instruments date to Leon Battista Alberti around 1450, although designs evolved greatly afterwards. Modern anemometers may use rotating cups, propellers, heated wires or ultrasonic sensors for measurements.
Q86. Which scientist proposed that electrons can move in certain stable atomic orbits without continuously radiating energy?
[UPSC NDA – 2024]
(A) Ernest Rutherford
(B) J. J. Thomson
(C) Niels Bohr
(D) Albert Einstein
Answer: (C) Niels Bohr
Explanation: Niels Bohr’s 1913 atomic model introduced permitted electron orbits or energy levels. Electrons emit or absorb light when transitioning between levels, rather than losing energy continuously in a stationary state. This addressed an important weakness in Rutherford’s earlier model.
Q85. Which statement correctly describes James Watt’s contribution to the Industrial Revolution?
[UPSC NDA – 2024]
(A) Thomas Savery invented the astrolabe
(B) Thomas Newcomen invented synthetic dyes
(C) James Watt improved the steam engine so it could power factories, not merely pump water
(D) Matthew Boulton discovered the refining of gold
Answer: (C) James Watt improved the steam engine so it could power factories, not merely pump water
Explanation: James Watt improved steam-engine efficiency, notably through the separate condenser, making broader industrial use economical. Earlier engines were largely employed to pump water from mines. Watt’s refinements supported factory power and machinery during the Industrial Revolution.
Q84. Who experimentally demonstrated electromagnetic waves, supporting Maxwell’s theory, by producing and detecting radio waves in the 1880s?
[SSC CHSL – 2024]
(A) Heinrich Hertz
(B) William Hopkins
(C) Guglielmo Marconi
(D) Michael Faraday
Answer: (A) Heinrich Hertz
Explanation: Heinrich Hertz generated and detected electromagnetic waves in laboratory experiments during the late 1880s. His observations confirmed James Clerk Maxwell’s predictions that changing electric and magnetic fields propagate as waves. The unit of frequency, hertz, honours him.
Q83. Who discovered the principle that an immersed body experiences an upward force equal to the weight of displaced fluid?
[SSC CPO – 2024]
(A) Niels Bohr
(B) Isaac Newton
(C) Galileo Galilei
(D) Archimedes
Answer: (D) Archimedes
Explanation: Archimedes’ principle explains buoyancy as the upward force exerted by a fluid on an immersed object. This force equals the weight of fluid displaced. The principle helps determine whether objects float, sink or remain suspended in liquids.
Q82. Who discovered the black reaction, a staining method that reveals the structure of entire neurons?
[SSC JE (Civil) – 2024]
(A) Robert Remak
(B) Albert Kölliker
(C) Camillo Golgi
(D) Jacques Loeb
Answer: (C) Camillo Golgi
Explanation: Camillo Golgi developed a silver-chromate staining technique in 1873 that made individual nerve cells visible against a comparatively clear background. This black reaction revolutionized microscopic study of neurons and enabled later advances in understanding nervous-system structure.
Q81. Who shared the 2005 Nobel Prize in Physiology or Medicine with Barry Marshall for discovering the bacterium associated with gastric ulcers?
[SSC JE (Electrical) – 2024]
(A) Jean-Paul Vuillemin
(B) Robert Koch
(C) Félix-Archimède Pouchet
(D) Robin Warren
Answer: (D) Robin Warren
Explanation: Robin Warren and Barry Marshall demonstrated that Helicobacter pylori plays a major role in gastritis and many peptic ulcers. Their discovery challenged the belief that ulcers resulted mainly from stress or excess acid, opening the way for antibiotic-based treatment.
