2018

231. Graphite is a good conductor of electricity. It is because of its

Graphite is a good conductor of electricity. It is because of its

[amp_mcq option1=”linear structure” option2=”tetrahedral structure” option3=”triangular planar structure” option4=”hexagonal multilayer structure” correct=”option4″]

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Graphite is a good conductor of electricity because of its structure. It consists of layers of carbon atoms arranged in a hexagonal lattice. Within each layer, carbon atoms are bonded covalently, with each carbon atom bonded to three others. This $sp^2$ hybridization leaves one unhybridized p-orbital per carbon atom, which overlaps with adjacent p-orbitals to form a delocalized pi electron system across the entire layer. These delocalized electrons are mobile and can carry electric charge, making the layers conductive. The overall structure is described as hexagonal multilayer, which creates the environment for these delocalized electrons.
The electrical conductivity of graphite is due to the presence of delocalized electrons in its layered hexagonal structure.
The layers in graphite are weakly bonded by Van der Waals forces, allowing them to slide easily, which is why graphite is soft and used as a lubricant. This contrasts with diamond, which has a rigid tetrahedral structure with all valence electrons localized in sigma bonds, making it an electrical insulator.

232. Which one of the following is an eco-friendly solvent ?

Which one of the following is an eco-friendly solvent ?

[amp_mcq option1=”Liquid ammonia” option2=”Carbon disulphide” option3=”Benzene” option4=”Water” correct=”option4″]

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An eco-friendly or green solvent minimizes environmental impact. Water is considered the most eco-friendly solvent due to its abundance, low cost, non-toxicity, non-flammability, and lack of harmful vapours. Other options are less environmentally friendly: Liquid ammonia is corrosive and toxic. Carbon disulphide is toxic, highly flammable, and volatile. Benzene is a known carcinogen, toxic, and volatile.
Water is widely regarded as the most eco-friendly solvent.
Green chemistry aims to design chemical products and processes that reduce or eliminate the use and generation of hazardous substances. Choosing appropriate solvents is a key aspect of green chemistry.

233. Which one of the following gases is not responsible for global warming

Which one of the following gases is not responsible for global warming ?

[amp_mcq option1=”Water vapour” option2=”Chlorofluorocarbons” option3=”Nitrogen” option4=”Methane” correct=”option3″]

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Greenhouse gases are atmospheric gases that absorb and emit infrared radiation, contributing to the greenhouse effect and thus global warming. Common greenhouse gases include water vapour (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), ozone (O3), and chlorofluorocarbons (CFCs). Nitrogen (N2), despite being the most abundant gas in Earth’s atmosphere, is a diatomic molecule that does not significantly absorb infrared radiation and is therefore not considered a greenhouse gas.
Nitrogen (N2) is not a greenhouse gas.
The greenhouse effect is a natural process essential for maintaining the Earth’s temperature, but human activities have increased the concentration of greenhouse gases, leading to enhanced warming. While N2 is not a greenhouse gas, some nitrogen compounds like N2O are potent greenhouse gases.

234. An acid solution of pH equal to three is gradually diluted with water.

An acid solution of pH equal to three is gradually diluted with water. As a result of this dilution, the pH of the solution will

[amp_mcq option1=”reach near to zero.” option2=”reach near to fourteen.” option3=”reach near to seven.” option4=”remain unchanged.” correct=”option3″]

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An acid solution with pH = 3 has a relatively high concentration of H+ ions. Diluting this solution with pure water (which has a neutral pH of 7) reduces the concentration of the acid, and thus the concentration of H+ ions from the acid. The total concentration of H+ ions approaches the concentration of H+ ions in pure water (which is $10^{-7}$ M at 25°C, corresponding to pH 7). As the concentration of H+ decreases, the pH value (which is -log[H+]) increases. The pH will move from 3 towards 7, but it will not exceed 7 when diluting with pure water.
Diluting an acidic solution with neutral water increases its pH, moving it towards 7.
Similarly, diluting a basic solution with neutral water decreases its pH, moving it towards 7. The pH of a solution being diluted with pure water will approach the pH of pure water (7), but will not cross the neutrality point unless the original solution was extremely concentrated or involved complex acid-base equilibria not typical for this type of question.

235. Consider the following statement : “When a body is in equilibrium, the

Consider the following statement :
“When a body is in equilibrium, the sum of the clockwise moments about any point equals the sum of the anticlockwise moments about the same point.”
Which one of the following laws is described in the above statement ?

[amp_mcq option1=”Law of motion” option2=”Law of moments” option3=”Law of momentum” option4=”Law of magnetism” correct=”option2″]

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The statement “When a body is in equilibrium, the sum of the clockwise moments about any point equals the sum of the anticlockwise moments about the same point” is the definition of rotational equilibrium. This condition is formally known as the Law of Moments, which is part of the requirements for a body to be in complete equilibrium (the other part being translational equilibrium, i.e., zero net force).
The Law of Moments is the principle that governs rotational equilibrium.
Moment (or torque) is the tendency of a force to cause rotation around an axis or pivot point. For a body to be in complete mechanical equilibrium, both the net force and the net moment acting on it must be zero.

236. Which of the following statements regarding temperature of an object i

Which of the following statements regarding temperature of an object in Kelvin scale is/are correct ?

  • 1. It can be a negative, zero or positive quantity.
  • 2. It can either be a negative or a positive quantity.
  • 3. It can never be negative.
  • 4. It can be a positive definite quantity.

Select the correct answer using the code given below :

[amp_mcq option1=”1 and 2 only” option2=”2 and 4 only” option3=”3 and 4 only” option4=”4 only” correct=”option3″]

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The Kelvin scale is an absolute temperature scale. The zero point (0 K) is absolute zero, the theoretical lowest possible temperature. Temperatures on the Kelvin scale are always non-negative (greater than or equal to zero).
Statement 1: Incorrect, as Kelvin temperature cannot be negative.
Statement 2: Incorrect, as Kelvin temperature cannot be negative and can be zero.
Statement 3: Correct, Kelvin temperature can never be negative (it is always $\ge 0$).
Statement 4: Interpreting “positive definite quantity” in this context to mean a quantity that is positive or zero (non-negative), this statement is correct, as Kelvin temperature is always $\ge 0$. If interpreted strictly as strictly positive (> 0), it would be incorrect as 0 K is possible. Given the options, the non-negative interpretation is most likely intended for statement 4, making both 3 and 4 correct.
Temperature on the Kelvin scale is always non-negative ($\ge 0$).
Absolute zero (0 K or -273.15 °C) is the point at which particles have minimum possible motion (though not zero motion according to quantum mechanics). The Kelvin scale is used extensively in scientific applications.

237. Which one of the following statements about the Principle of Calorimet

Which one of the following statements about the Principle of Calorimetry is correct ?

[amp_mcq option1=”It is always valid.” option2=”It is valid when temperature is constant.” option3=”It is valid only when there is no change of state.” option4=”It is valid only under equilibrium condition.” correct=”option1″]

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The Principle of Calorimetry is based on the law of conservation of energy. It states that in an isolated system, the total amount of heat lost by the hot bodies is equal to the total amount of heat gained by the cold bodies. This principle is fundamentally valid whenever heat exchange occurs in an isolated system, including processes involving changes of state (by accounting for latent heat) and processes involving temperature changes. Options B, C, and D state conditions under which the principle is *only* valid, which are incorrect limitations. The principle is valid even when temperature is not constant (during temperature change), when there is a change of state (by including latent heat), and it describes the process of heat exchange *towards* equilibrium, not only at equilibrium. Therefore, “It is always valid” (interpreted as valid in an isolated system for which it is defined) is the most accurate statement among the choices, as the other options describe false limitations.
The Principle of Calorimetry is based on energy conservation in thermal interactions and applies in isolated systems, irrespective of whether temperature changes or phase changes occur.
In practical calorimetry experiments, efforts are made to create an isolated system to minimize heat exchange with the surroundings and ensure the principle holds true for the components within the calorimeter.

238. Which one of the following determines the direction of induced current

Which one of the following determines the direction of induced current ?

[amp_mcq option1=”Fleming’s left hand rule” option2=”Fleming’s right hand rule” option3=”Feynman’s left hand rule” option4=”Right hand thumb rule” correct=”option2″]

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Fleming’s Right-Hand Rule is used to determine the direction of the induced electric current in a conductor when it is moved in a magnetic field or when the magnetic field around it changes. The thumb, forefinger, and middle finger are held mutually perpendicular: the thumb points in the direction of motion of the conductor, the forefinger points in the direction of the magnetic field, and the middle finger points in the direction of the induced current.
Fleming’s Right-Hand Rule determines the direction of induced current, while Fleming’s Left-Hand Rule determines the direction of force on a current-carrying conductor in a magnetic field.
The phenomenon of induced current is described by Faraday’s Law of electromagnetic induction, and its direction is governed by Lenz’s Law, which is encapsulated by Fleming’s Right-Hand Rule.

239. Which of the following statements about a body under equilibrium is/ar

Which of the following statements about a body under equilibrium is/are correct ?

  • 1. No forces are acting.
  • 2. A number of parallel forces may be acting.
  • 3. The law of moments must apply.

Select the correct answer using the code given below :

[amp_mcq option1=”1, 2 and 3″ option2=”2 and 3 only” option3=”1 and 3 only” option4=”2 only” correct=”option2″]

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A body is under equilibrium if the net force acting on it is zero (translational equilibrium) and the net torque acting on it is zero (rotational equilibrium).
Statement 1: “No forces are acting” is incorrect. Forces can be acting, but they must be balanced, meaning the vector sum of all forces is zero.
Statement 2: “A number of parallel forces may be acting” is correct. For example, if two equal and opposite parallel forces act on a body, they form a couple, which produces a torque. For the body to be in equilibrium, this torque must be balanced by other torques, and the net force must be zero (which these two forces satisfy). More generally, parallel forces can sum to zero net force and zero net torque.
Statement 3: “The law of moments must apply” is correct. The Law of Moments states that for rotational equilibrium, the sum of clockwise moments about any point equals the sum of anticlockwise moments about the same point. This is a necessary condition for a body to be in equilibrium.
Equilibrium requires zero net force and zero net torque. The Law of Moments describes the condition for zero net torque.
A body in equilibrium can be either at rest (static equilibrium) or moving with constant velocity (dynamic equilibrium). Both require the net force and net torque to be zero.

240. The X-chromosome linked colour blindness affects the ability to detect

The X-chromosome linked colour blindness affects the ability to detect the difference between which of the following lights ?

[amp_mcq option1=”Green light and red light” option2=”Yellow light and blue light” option3=”Blue light and violet light” option4=”Yellow light and red light” correct=”option1″]

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X-chromosome linked colour blindness is most commonly red-green colour blindness. This condition affects the photoreceptor cells in the eye (cones) that are sensitive to red and green light, making it difficult to distinguish between these colours.
X-linked colour blindness primarily impairs the ability to distinguish between red and green colours.
Colour blindness is often inherited and is much more prevalent in males because the genes responsible for the most common forms are located on the X chromosome. Females have two X chromosomes, so a functional gene on one X chromosome can often compensate for a non-functional one on the other, whereas males only have one X chromosome.
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