General Science - MCQ Online Test (1) - UPSC MCQ

Deficiency Leading to Dental Caries:
- Answer: B: Fluorine

Explanation:
- Dental caries, also known as tooth decay or cavities, occur when the hard, outer layer of the tooth (enamel) is damaged.
- Fluorine, in the form of fluoride, is an essential mineral for maintaining strong and healthy teeth.
- A deficiency of fluoride can lead to dental caries because it plays a crucial role in:
1. Remineralization: Fluoride helps to rebuild and strengthen tooth enamel by aiding in the remineralization process, which is the natural repair mechanism for tooth enamel.
2. Preventing demineralization: Fluoride inhibits the demineralization process, which is caused by acids produced by bacteria in plaque. This helps to protect teeth from decay.
3. Reducing bacterial activity: Fluoride can also reduce the ability of bacteria to produce acid, further protecting teeth from decay.

- It is important to ensure an adequate intake of fluoride through sources such as fluoridated water, toothpaste, mouthwashes, and, if necessary, dietary supplements. This helps to maintain optimal oral health and prevent dental caries.

Answer: d. Yellow colour Explanation: - Carotene is a natural pigment found in certain plants and animal products, including Indian cow's milk. - This pigment is responsible for the deep yellow to orange colour in various fruits, vegetables, and other food items, such as carrots, pumpkins, and sweet potatoes. - In Indian cow's milk, the presence of carotene gives the milk a distinct yellow colour. - Carotene is a precursor to Vitamin A, which is essential for maintaining good vision, immune system function, and overall health. - The yellow colour of the milk does not affect its nutritional value, and in fact, carotene-rich milk is considered to be beneficial for health due to its Vitamin A content.

Answer: C. Halophytes Explanation:

• Halophytes are plants that can tolerate and grow in saline water or high salt concentrations in the soil.
• They have developed special adaptations to survive in these harsh conditions, such as salt excretion through their leaves, salt accumulation in specialized cells, and the ability to maintain osmotic balance.
• Examples of halophytes include mangroves, seagrasses, and some species of salt marsh plants.
• Hydrophytes, on the other hand, are plants adapted to grow in water or very wet environments, while thallophytes are a diverse group of non-vascular plants such as algae and fungi. Mesophytes are plants that grow in moderately moist conditions.

Answer: C Explanation: Both statements A and B are correct. Let's break down each statement: Statement A: - Each codon specifies only one amino acid: This statement is correct. The genetic code is based on a set of three nucleotide bases (a triplet) that correspond to a specific amino acid. While it is true that multiple codons can code for the same amino acid (this is called degeneracy), each codon only codes for one specific amino acid. Statement B: - Amino acid codons are identical in human beings, tobacco plants, and viruses: This statement is also correct. The genetic code is said to be universal, meaning that it is almost the same in all organisms, from bacteria to humans. While there are some rare exceptions, the genetic code is generally conserved throughout all living organisms. This means that the same codons code for the same amino acids in humans, plants, and viruses.

Explanation: In protein synthesis in E. coli, when each amino acid is attached to a specific tRNA at the expense of ATP energy, the ion of the following element is used: - Magnesium (Mg²⁺): Magnesium ions play a crucial role in the catalytic activity of the enzymes involved in this process. They help stabilize the structures of tRNAs and aminoacyl-tRNA synthetases, allowing for the correct attachment of amino acids to their corresponding tRNA molecules. Additionally, magnesium ions facilitate the hydrolysis of ATP, which provides the energy needed for this reaction to take place.

Higher Intensity of Illumination:

Sodium vapor lamps are preferred over incandescent lamps mainly because of their higher intensity of illumination. Some reasons for this preference include:

• Efficiency: Sodium vapor lamps are more energy-efficient in comparison to incandescent lamps, meaning they produce more light per watt of electricity consumed.
• Longevity: The lifespan of sodium vapor lamps is significantly longer than that of incandescent lamps, reducing the need for frequent replacements and maintenance.
• Color Rendering: Sodium vapor lamps produce a very distinct yellow-orange light, which can be more suitable for certain applications like street lighting, where the focus is on visibility and not color accuracy.
• Low Operating Cost: Due to their energy efficiency and long life, the overall cost of operating sodium vapor lamps is lower than that of incandescent lamps.

While sodium vapor lamps do have some drawbacks, such as their warm-up time and limited color rendering capabilities, their higher intensity of illumination makes them a popular choice for various lighting applications.

Answer: B. Ammonium chloride Explanation: In an ordinary dry cell battery, the different components have specific functions: - Electrolyte: Ammonium chloride (NH4Cl) - Ammonium chloride is a salt that acts as the electrolyte in dry cell batteries. It facilitates the flow of ions between the anode and cathode, which is essential for the battery to function. - Anode: Zinc (Zn) - In a dry cell, the zinc container acts as the anode. It is the negative electrode, which provides electrons to the external circuit during discharge. - Cathode: Manganese dioxide (MnO2) - Manganese dioxide serves as the cathode, or positive electrode, in a dry cell. It receives electrons from the external circuit during discharge and reacts with the ammonium ions in the electrolyte. - Other components: Carbon rod and separator - A carbon rod is used as a current collector in the cathode, while a separator is used to prevent direct contact between the anode and cathode, thus preventing a short circuit. In summary, the electrolyte in an ordinary dry cell is ammonium chloride, which plays a crucial role in facilitating the flow of ions and enabling the battery to function.

Explanation The correct answer is B: Nickel and cadmium. Here is a brief explanation of the different types of batteries and their electrodes: - Nickel-Cadmium (NiCd) batteries: These rechargeable batteries are commonly used in devices such as torch lights and electric shavers. The electrodes in these batteries are made of nickel (positive electrode) and cadmium (negative electrode). - Iron and cadmium: This combination is not commonly used in rechargeable batteries. - Lead peroxide and lead: These are the electrode materials for lead-acid batteries, which are typically used in automotive applications, such as car batteries. - Zinc and carbon: These are the electrode materials in non-rechargeable zinc-carbon batteries, which are typically used in low-power applications such as remote controls and clocks.

Answer: A Explanation: Mixed oxide fuel (MOX) is a type of nuclear fuel that consists of a blend of uranium and plutonium oxides. It is mainly used for the following purposes: - Nuclear Reactors: MOX fuel is primarily used in nuclear reactors to generate electricity. It can be utilized in both light water reactors (LWRs) and fast breeder reactors (FBRs). In LWRs, MOX fuel can replace conventional low-enriched uranium (LEU) fuel, while in FBRs, it can help generate more plutonium to sustain the breeding cycle. - Resource Optimization: Using MOX fuel can help optimize the use of nuclear resources by recycling plutonium from spent nuclear fuel and reducing the quantity of high-level radioactive waste. - Non-Proliferation: The use of MOX fuel can contribute to non-proliferation efforts by reducing the stockpiles of weapons-grade plutonium and converting it into a less proliferation-sensitive form. Thus, mixed oxide fuel is primarily used for nuclear reactors and not for aero planes, cryogenic engines, or PSLV rockets.

Explanation:

Acid rain is caused by the pollution of the environment by:

• Nitrous oxide (NOx): This gas is released from various human activities, such as burning fossil fuels in vehicles, power plants, and industrial processes.
• Sulphur dioxide (SO2): This gas is primarily released from the burning of coal and oil in power plants and other industrial processes, as well as from volcanic eruptions and other natural sources.

When these gases are released into the atmosphere, they react with water, oxygen, and other chemicals to form acidic compounds. These compounds then fall back to the Earth's surface as acid rain, which can have harmful effects on soil, water, forests, and aquatic life.

Answer: A. Density Explanation: - Clouds are composed of tiny water droplets or ice crystals that are suspended in the atmosphere. - These water droplets and ice crystals are lighter than the surrounding air, which is why they can float. - The density of the cloud particles is lower than the density of the surrounding air, which allows them to stay suspended in the atmosphere. - The buoyancy force, which is the force that opposes gravity, helps keep the cloud particles afloat. This force is directly proportional to the density difference between the cloud particles and the surrounding air. - The temperature, velocity, and pressure of the clouds also play a role in their behavior, but it is primarily the density difference that allows them to float in the atmosphere.

Answer: C: Ethyl alcohol Explanation: - Fermentation is a metabolic process in which microorganisms, such as yeast or bacteria, convert carbohydrates (e.g., sugar) into simpler compounds like acids, gases, or alcohols, under anaerobic conditions (without the presence of oxygen). - The most common end product of fermentation is ethyl alcohol (also known as ethanol) and carbon dioxide. - This process is widely used in the production of alcoholic beverages, such as beer, wine, and spirits, as well as in the production of biofuels and some industrial chemicals. - In the specific case of yeast fermentation, the following reaction occurs: C6H12O6 (glucose) → 2 C2H5OH (ethyl alcohol) + 2 CO2 (carbon dioxide) - Other fermentation processes may yield different end products, such as lactic acid in lactate fermentation or acetic acid in acetate fermentation. However, ethyl alcohol is the most common end product in fermentation.

Answer: B: Silver bromide Explanation: Role of Silver Bromide in Photography:

• Photographic film: Silver bromide is a light-sensitive compound that is widely used in the production of photographic film. When exposed to light, the silver ions in silver bromide crystals are reduced to metallic silver, creating a visible image.
• Black and white photography: In black and white photography, silver bromide is used as the primary light-sensitive material. When the film is developed, the exposed silver bromide crystals are reduced to metallic silver, creating a visible image. The unexposed crystals are then removed through a fixing process, leaving behind a stable, black and white image.
• Photographic paper: Silver bromide is also used in the production of photographic paper, which is used to make prints of photographic negatives. The paper is coated with a light-sensitive emulsion containing silver bromide, which reacts to the light projected through the negative during the printing process, creating a visible image on the paper.

Overall, silver bromide is a crucial chemical used in the field of photography due to its light-sensitive properties, which enable the creation of images on photographic film and paper.

Answer: C. Ammonia Explanation: - Ammonia (NH3) is commonly used as the refrigerant gas in domestic refrigerators. - This is because ammonia has several desirable properties for refrigeration systems: - Low boiling point: Ammonia's low boiling point allows it to absorb heat efficiently and provide effective cooling. - High thermal conductivity: This property enables ammonia to transfer heat effectively, making it a good choice for cooling systems. - Non-flammable: Unlike some other refrigerant gases, ammonia is not flammable, which reduces the risk of fire in refrigeration systems. - Environmentally friendly: Ammonia has zero ozone depletion potential and low global warming potential, making it an environmentally responsible choice for refrigeration. - However, ammonia is also toxic and has a strong odor, so it must be used in well-ventilated areas and contained within the refrigeration system.

Answer: A. Red phosphorus

Explanation:

• Match sticks are made using red phosphorus, which is a component of the match head.
• Red phosphorus is a highly reactive and flammable chemical element that provides the necessary ignition for the match to light when struck against a suitable surface.
• Along with red phosphorus, other chemicals like potassium chlorate, sulfur, and glue are also used in the match head to ensure proper ignition and burning.
• Blue phosphorus and lead nitrate are not used in making match sticks, and therefore options B and C are incorrect.

Ans: a

Explanation: When a particle or a body moves with a uniform speed v on a circular path of radius r, then it is acted upon by a force mv²/r which is always directed towards the centre of the circle. This force is called centripetal force

Ans: b

Explanation: The value of escape velocity does not depend upon the mass of the projected body; instead it depends on the mass and radius of the planet from which it is being projected. The value of escape velocity does not depend on the angle and direction of projection

Ans: d

Explantion: Fuse Wire is used in a circuit to control the maximum current flowing in a circuit. It is a thin wire having high resistance and is made up of a material with low melting point.

Ans: c

Explanation: When a lawn roller is pulled by applying a force along the handle at an acute angle, work done by applied force is (+) ve.

Ans: b

Explanation: Convex mirrors are commonly used as rear-view (wing) mirrors in vehicles. These mirrors are fitted on the sides of the vehicle, enabling the driver to see traffic behind him/her to facilitate safe driving. Convex mirrors are preferred because they always give an erect, though diminished, image. Also, they have a wider field of view as they are curved outwards. Thus, convex mirrors enable the driver to view much large area than would be possible with a plane mirror.

Explanation: An air bubble in water behaves as a concave lens due to the following reasons: - Refractive indices: The refractive index of air is lower than that of water. When light passes through the air bubble, it moves from a medium of higher refractive index (water) to a medium of lower refractive index (air), and then back into the water. - Light bending: Due to the difference in refractive indices, light rays bend away from the normal (the imaginary line perpendicular to the surface) when entering the air bubble, and then bend towards the normal when exiting the air bubble. This bending causes the light rays to diverge, which is a characteristic of concave lenses. - Shape of the air bubble: The air bubble is usually spherical in shape. When light passes through the curved surface of the air bubble, it results in the divergence of the light rays similar to a concave lens. In conclusion, an air bubble in water behaves as a concave lens due to the difference in refractive indices of air and water, the bending of light rays, and the spherical shape of the air bubble.

Ans: b

Explanation: If the lens is immersed in a medium having refractive index equal to that of the lens, then

The lens becomes invisible.

The lens behaves as a plane glass plate.

The focal length becomes infinite.

Ans: a

Explanation: Sound travels in the form of waves. Sound waves are longitudinal waves. Thus, they do not exhibit polarisation.

Ans: b

Explanation: Amplitude – the maximum displacement on one side of mean position of a particle of medium, is called the amplitude of the wave.

Time period -the time taken by a particle of the medium to complete its one vibration in called the time period of the wave.

Frequency -the number of vibrations made by a particle is called the frequency of the wave.

Wave velocity - the distance travelled by a wave in one second is travelled by a wave in one second is called wave velocity.

Wavelength - the distance travelled by a wave in one time period of a medium is called its wavelength.

Ans: b

Explanation: Tension in the string of simple pendulum is always perpendicular to the displacement of the bob, hence it is zero.