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Question 629

Which one of the following is a chemical change ?

ABurning of candle

BMelting of wax

CVapourisation of water

DMagnetising of Iron

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A. Burning of candleExplanation: The burning of a candle is a chemical change because new substances such as carbon dioxide, water vapour, and heat energy are produced during the reaction between wax and oxygen. This change is irreversible and results in a permanent alteration of the chemical composition of the material. In contrast, melting of wax and vapourisation of water are physical changes since no new substances are formed and the process can be reversed by cooling.

Question 628

Sound travels fastest in

AVacuum

BSteel

CWater

DAir

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B. SteelExplanation: Sound travels fastest in steel because it is a solid material where the particles are packed very closely together. Sound waves need a medium to travel, and their speed depends on how quickly vibrations can pass from one particle to another. In solids, particles are tightly bound, so vibrations are transmitted more efficiently. In contrast, sound travels slower in liquids and slowest in gases. It cannot travel through a vacuum because there are no particles to carry the vibrations.

Question 627

Aurora Borealis is a light phenomenon seen at night in the:

ANorthern hemisphere

BEquatorial region

CBarmunda Triangle region

DNone of these

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A. Northern hemisphereExplanation: Aurora Borealis, also known as the Northern Lights, is a natural light phenomenon visible mainly in the northern hemisphere, near the Arctic regions. It occurs when charged particles from the solar wind interact with gases like oxygen and nitrogen in the Earth's upper atmosphere (ionosphere). These collisions release energy in the form of colorful lights, usually green, pink, red, or violet. A similar phenomenon in the southern hemisphere is called the Aurora Australis or Southern Lights.

Question 626

The weight of a person on the surface of the moon will be about one-sixth of his weight on the surface of the earth. This is because

AThe moon has no air.

BThe moon has no water.

CThe gravity of the moon is about half of the earth.

DThe gravity of the moon is abouut one-sixth of that of the earth.

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D. The gravity of the moon is abouut one-sixth of that of the earth.Explanation: The weight of a person depends on the gravitational force exerted by a celestial body. The Moon’s gravity is only about 1/6th that of the Earth’s because it has much less mass and a smaller radius. Therefore, an object or person weighing 60 kg on Earth would weigh only about 10 kg on the Moon. Although mass remains constant everywhere, weight changes according to the local gravitational acceleration (g). Hence, lower gravity results in lower weight on the Moon.

Question 610

Measles is a disease caused by :

ABacteria

BProtozoa

CWorm

DVirus

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D. VirusExplanation: Measles is a highly contagious disease caused by the Measles virus, which belongs to the Paramyxoviridae family, genus Morbillivirus. It spreads through respiratory droplets from coughing or sneezing by an infected person. Common symptoms include high fever, cough, runny nose, red eyes, and a characteristic red skin rash. Severe cases can lead to pneumonia or encephalitis. Measles can be effectively prevented by the MMR vaccine (Measles, Mumps, and Rubella).

Question 609

A solar eclipse occurs when the :

Aearth comes between the Sun and the Moon

BSun comes between the earth and the moon

CMoon is at right angle to the earth

DMoon comes between the Sun and the Earth

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D. Moon comes between the Sun and the EarthExplanation: A solar eclipse occurs when the Moon comes between the Sun and the Earth and casts its shadow on the Earth. This happens during the new moon phase, when all three celestial bodies are almost in a straight line. Depending on the alignment, the eclipse can be total (Sun completely covered), partial (Sun partially covered), or annular (ring-shaped Sun visible). During this event, sunlight is blocked for a short time in specific areas of the Earth’s surface.

Question 465

Which layer of the atmosphere is nearest to the surface of the earth?

AMesosphere

BThermosphere

CTroposphere

DStratosphere

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C. TroposphereExplanation: The troposphere is the lowest layer of the Earth's atmosphere and is closest to the Earth's surface. It extends up to about 8–15 km from the surface, depending on latitude and season. This layer contains about 75% of the total atmospheric mass and almost all the water vapor and weather phenomena such as clouds, rain, and storms occur here. The temperature decreases with increasing altitude in this layer. The boundary between the troposphere and the stratosphere is known as the tropopause.

Question 464

Rickets is a disease caused by the deficiency of

AVitamin- K

BVitamin- D

CVitamin- B1

DVitamin- A

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B. Vitamin- DExplanation: Rickets is a bone disease caused by the deficiency of Vitamin D in children. Vitamin D is essential for the proper absorption of calcium and phosphorus from the intestine, which are vital for healthy bone formation. Its deficiency leads to weak and soft bones, resulting in deformities such as bowed legs and knock knees. The adult form of this disease is known as osteomalacia. Vitamin D can be obtained from sunlight, fish oil, eggs, and fortified milk.

Question 463

Which of the following diseases is not caused by bacteria?

ACholera

BTyphoid

CTuberculosis

DChickungunya

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D. ChickungunyaExplanation: Chikungunya is a viral disease caused by the Chikungunya virus, which belongs to the Togaviridae family. It is transmitted to humans through the bite of infected Aedes aegypti and Aedes albopictus mosquitoes. The disease causes sudden fever, joint pain, headache, and rash. In contrast, cholera (caused by Vibrio cholerae), typhoid (by Salmonella typhi), and tuberculosis (by Mycobacterium tuberculosis) are all bacterial diseases.

Question 462

Thyroid gland is located

Anear the heart

Bat the base of the brain

Cbelow the liver

Din the neck region

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D. in the neck regionExplanation: The thyroid gland is located in the neck region, just below the larynx (voice box) and in front of the trachea (windpipe). It is a butterfly-shaped endocrine gland that secretes the hormones thyroxine (T₄) and triiodothyronine (T₃). These hormones regulate metabolism, growth, and energy production in the body. The thyroid also produces calcitonin, which helps control calcium levels in the blood. Iodine is essential for the synthesis of thyroid hormones.

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Science

Which one of the following is a chemical change ?

Sound travels fastest in

Aurora Borealis is a light phenomenon seen at night in the:

The weight of a person on the surface of the moon will be about one-sixth of his weight on the surface of the earth. This is because

Measles is a disease caused by :

A solar eclipse occurs when the :

Which layer of the atmosphere is nearest to the surface of the earth?

Rickets is a disease caused by the deficiency of

Which of the following diseases is not caused by bacteria?

Thyroid gland is located

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