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Atmospheric Chemistry
What is the unit used to measure the quantity of ozone in the atmosphere?
The quantity of ozone in the atmosphere is commonly measured in Dobson Units (DU), which represent the thickness of the ozone layer if compressed to standard temperature and pressure. Dalton is a unit of atomic mass, Coulomb measures electric charge, and 'none' is not a valid unit here.
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Human Biology
The temperature of a dead body is ____?
After death, a body's temperature gradually adjusts to the ambient temperature of its surroundings, as metabolic heat production ceases. Therefore, the temperature of a dead body eventually becomes the temperature of the place where it is kept.
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Waves And Their Applications
The principle used in radar is the same as that of sonar. In radar, we use radio waves; whereas in sonar, we use?
Radar uses radio waves to detect objects by reflecting these waves, while sonar uses ultrasonic waves (high-frequency sound waves) to detect objects underwater by echo location. Therefore, the correct answer is ultrasonic.
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Thermal Properties Of Materials
In winter, an iron pipe feels colder than a wooden window. This is because wood is ____?
Wood is a non-conductor (insulator) of heat, so it does not transfer heat away from your hand as quickly as iron, making it feel warmer. Iron, being a good conductor, transfers heat rapidly, making it feel colder to the touch in winter.
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Fermentation
Yeast is used in making bread because it produces ____?
Yeast ferments sugars in the dough and produces carbon dioxide gas, which causes the bread to rise and become fluffy. This is why carbon dioxide is the correct answer.
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Vision And Lenses
Short-sightedness can be corrected by using ____?
Short-sightedness (myopia) occurs when the eye focuses images in front of the retina. It is corrected using a concave lens, which diverges light rays so that they focus correctly on the retina.
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Temperature Conversion
A Fahrenheit thermometer indicates a temperature of 14°F. What is the corresponding reading on the Celsius scale?
The formula to convert Fahrenheit to Celsius is C = (F - 32) × 5/9. Substituting 14 for F gives C = (14 - 32) × 5/9 = (-18) × 5/9 = -10°C. Therefore, the correct Celsius equivalent of 14°F is -10°C, which corresponds to option B.
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Radioactivity
The half-life of a radioactive element is 8 days. How long does it take to reduce it from 10 mg to 5 mg?
The half-life of a radioactive element is the time required for half of the substance to decay. Since the half-life is 8 days, it takes exactly 8 days for 10 mg to reduce to 5 mg.
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Thermal Expansion In Rails
In a railway track, two rails are joined end to end with a gap in between them because?
Rails are joined with a small gap to allow for thermal expansion during hot weather. Without this gap, the rails could expand and buckle, causing accidents. Hence, the gap prevents accidents due to expansion in summer.
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Human Nutrition
Which of the following vitamins promotes healthy functioning of the eyes in human beings?
Vitamin A is essential for maintaining healthy vision and proper functioning of the eyes. It helps form the pigment rhodopsin, which is necessary for low-light and color vision.