UPSC CDS-1

21. Which of the following endocrine glands is not found in pair in

Which of the following endocrine glands is not found in pair in humans?

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Adrenal
Pituitary
Testis
Ovary
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Most major endocrine glands in the human body are either single structures or paired. Let’s examine the options: Adrenal glands are located on top of each kidney, hence there is a pair. Testes are the male gonads, typically a pair. Ovaries are the female gonads, typically a pair. The pituitary gland is located at the base of the brain, inferior to the hypothalamus, and is a single structure.
The pituitary gland is a single endocrine gland responsible for producing and regulating many hormones that control various bodily functions, including growth, metabolism, and reproduction. Other unpaired endocrine glands include the pineal gland, hypothalamus (neuroendocrine function), and pancreas (has endocrine and exocrine functions). Paired endocrine glands include the adrenal glands, testes (in males), and ovaries (in females).
The thyroid gland and parathyroid glands are also considered endocrine glands. The thyroid gland is typically a single, bilobed structure, but functionally it can be seen as a single unit. The parathyroid glands are typically four small glands, usually found in pairs on the back of the thyroid.

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22. Which one of the following is the correct sequence of organs that occu

Which one of the following is the correct sequence of organs that occur in the path of urine flow in human body?

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Kidney, ureter, urinary bladder, urethra
Kidney, urinary bladder, ureter, urethra
Kidney, ureter, urethra, urinary bladder
Urinary bladder, kidney, urethra, ureter
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The urinary system in humans produces, stores, and eliminates urine. Urine is formed in the kidneys through filtration and reabsorption processes. From the kidneys, urine travels down two tubes called ureters to reach the urinary bladder, a muscular sac that stores urine. When the bladder is full, urine is expelled from the body through a tube called the urethra.
The correct sequence of organs in the path of urine flow is: Kidney $\rightarrow$ Ureter $\rightarrow$ Urinary Bladder $\rightarrow$ Urethra. Any other order would be incorrect based on the physiological process of urine formation, transport, storage, and elimination.
The kidneys are the primary organs of the urinary system, filtering blood to produce urine. The ureters are conduits. The urinary bladder is a temporary reservoir. The urethra is the final passage out of the body. This sequence ensures that urine is collected and stored before voluntary or involuntary expulsion.

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23. The electromagnetic waves, which are used for satellite communication,

The electromagnetic waves, which are used for satellite communication, are

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infrared radiations
ultraviolet radiations
radio waves
visible lights
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Satellite communication relies on electromagnetic waves that can travel through the Earth’s atmosphere and the vacuum of space with minimal attenuation and interference. Radio waves, particularly in the microwave frequency range, are ideal for this purpose. These frequencies allow for high bandwidth transmission and can penetrate the ionosphere and lower atmosphere effectively.
Infrared radiation is used for shorter-range communication like remote controls or fiber optics but is not suitable for long-distance satellite communication due to atmospheric absorption. Ultraviolet radiation is largely absorbed by the atmosphere and is not used for this purpose. Visible light is also affected by atmospheric conditions (clouds, scattering) and is generally not used for long-distance space communication, although optical communication with satellites is an emerging technology. Radio waves/microwaves are the standard for current satellite communication systems.
Different frequency bands within the radio/microwave spectrum are allocated for various types of satellite communication, including C-band, Ku-band, Ka-band, etc., depending on the application (e.g., broadcasting, telecommunications, navigation).

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24. The resistivity $\rho$ of a material may be expressed in units of

The resistivity $\rho$ of a material may be expressed in units of

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ohm
ohm/cm
ohm-cm
ohm-cm$^2$
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Resistivity ($\rho$) is a fundamental property of a material that quantifies how strongly it resists the flow of electric current. Resistance ($R$) of a conductor is related to its resistivity, length ($L$), and cross-sectional area ($A$) by the formula $R = \rho \frac{L}{A}$. Rearranging this formula to solve for $\rho$, we get $\rho = R \frac{A}{L}$.
The unit of resistance ($R$) is Ohm ($\Omega$). The unit of area ($A$) is typically square meters (m²) or square centimeters (cm²). The unit of length ($L$) is typically meters (m) or centimeters (cm). Substituting these units into the formula for $\rho$: $\text{Units of } \rho = \Omega \times \frac{\text{cm}^2}{\text{cm}} = \Omega \cdot \text{cm}$. Alternatively, using meters: $\text{Units of } \rho = \Omega \times \frac{\text{m}^2}{\text{m}} = \Omega \cdot \text{m}$. Therefore, the resistivity is commonly expressed in ohm-centimeters ($\Omega \cdot \text{cm}$) or ohm-meters ($\Omega \cdot \text{m}$).
While both ohm-meter ($\Omega \cdot \text{m}$) and ohm-centimeter ($\Omega \cdot \text{cm}$) are valid units for resistivity, ohm-centimeter is also widely used, particularly in semiconductor physics and some older standards. Option C correctly identifies ohm-cm as a unit for resistivity.

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25. If $x$ is the temperature of a system in Kelvin and $y$ is the tempera

If $x$ is the temperature of a system in Kelvin and $y$ is the temperature of the system in ${}^\circ\text{C}$, then the correct relation between them is

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$x = 273 - y$
$x = 273 + y$
$x = 173 + y$
$x = 173 - y$
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The Kelvin and Celsius scales are two common temperature scales. The relationship between a temperature in Celsius ($y$) and the corresponding temperature in Kelvin ($x$) is given by the formula $x = y + 273.15$. For most practical purposes and in common examinations, this is often simplified to $x = y + 273$.
The Kelvin scale is an absolute temperature scale, with 0 K being absolute zero. The Celsius scale is a relative scale where 0°C is the freezing point of water and 100°C is the boiling point of water (at standard atmospheric pressure). A change of 1 degree Celsius is equal to a change of 1 Kelvin.
The formula $x = y + 273$ implies that a temperature of 0°C is equivalent to 273 K, and a temperature of 100°C is equivalent to 373 K. Absolute zero, which is -273.15°C, is equivalent to 0 K.

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26. Silver articles become black after some time when exposed to air

Silver articles become black after some time when exposed to air because

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silver gets oxidized to silver oxide
silver reacts with moist carbon dioxide in the air to form silver carbonate
silver reacts with sulphur in the air to form a coating of silver sulphide
silver reacts with nitrogen oxides in the air to form silver nitrate
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Silver articles tarnish and become black when exposed to air primarily due to a reaction with small amounts of sulfur compounds (like hydrogen sulfide, H₂S) present in the atmosphere. This reaction forms a thin layer of silver sulfide (Ag₂S) on the surface, which is black.
– Silver reacts with sulfur compounds in the air.
– The reaction produces silver sulfide (Ag₂S).
– Silver sulfide is black, causing the tarnish.
While silver can react with oxygen at high temperatures to form silver oxide, the black tarnish at room temperature is predominantly due to the formation of silver sulfide. Sources of hydrogen sulfide in the air include pollution, volcanic activity, and the decomposition of organic matter.

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27. The number of water molecules associated with copper sulphate molecule

The number of water molecules associated with copper sulphate molecule to form crystals is

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2
4
5
6
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Copper sulphate commonly exists as a hydrate with the chemical formula CuSO₄ · 5H₂O. This form is copper(II) sulfate pentahydrate, which is bright blue. The notation ‘· 5H₂O’ indicates that there are 5 water molecules associated with each unit of copper sulphate in the crystal lattice. These water molecules are called water of crystallization.
– Crystalline copper sulphate is a hydrate.
– The formula of common copper sulphate crystals is CuSO₄ · 5H₂O.
– This means 5 water molecules are associated with each CuSO₄ unit.
Anhydrous copper sulphate (CuSO₄), which has no water of crystallization, is white. When water is added to anhydrous copper sulphate, it forms the blue pentahydrate, and this reaction is exothermic. This property makes anhydrous copper sulphate useful as a test for the presence of water.

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28. Match List-I with List-II and select the correct answer using the code

Match List-I with List-II and select the correct answer using the code given below the Lists :

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List-I
(Name)		 List-II
(Formula)
A. Bleaching powder 1. NaHCO3
B. Baking soda 2. Na2CO3 · 10H2O
C. Washing soda 3. Ca(OH)2
D. Slaked lime 4. CaOCl2

Code :

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A-4, B-1, C-2, D-3
A-4, B-2, C-1, D-3
A-3, B-2, C-1, D-4
A-3, B-1, C-2, D-4
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Matching the names with their correct chemical formulas:
– Bleaching powder is Calcium oxychloride, formula CaOCl₂. (A-4)
– Baking soda is Sodium bicarbonate or Sodium hydrogen carbonate, formula NaHCO₃. (B-1)
– Washing soda is Sodium carbonate decahydrate, formula Na₂CO₃ · 10H₂O. (C-2)
– Slaked lime is Calcium hydroxide, formula Ca(OH)₂. (D-3)
The correct matching is A-4, B-1, C-2, D-3.
– Bleaching powder: CaOCl₂
– Baking soda: NaHCO₃
– Washing soda: Na₂CO₃ · 10H₂O
– Slaked lime: Ca(OH)₂
Quicklime is Calcium oxide (CaO). When quicklime reacts with water, it forms slaked lime (Calcium hydroxide, Ca(OH)₂). Bleaching powder is manufactured by passing chlorine gas over dry slaked lime. Baking soda is used in baking as a leavening agent. Washing soda is used in laundry detergents and for softening water.

29. Mahatma Gandhi’s Dandi March, a great event in Indian freedom struggle

Mahatma Gandhi’s Dandi March, a great event in Indian freedom struggle, was associated with

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iron
sodium chloride
sulphur
aluminium
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Mahatma Gandhi’s Dandi March, also known as the Salt March, was a nonviolent protest against the British salt tax. The tax made it illegal for Indians to collect or sell salt, forcing them to buy it from the British. The march culminated in Gandhi and his followers collecting salt from the seacoast at Dandi, symbolically breaking the British law. Common salt is primarily sodium chloride (NaCl).
– The Dandi March was a protest against the British salt monopoly and tax.
– The act of civil disobedience involved making salt from seawater.
– Salt is chemically primarily sodium chloride.
The Dandi March began on March 12, 1930, and ended on April 6, 1930. It was a significant campaign of nonviolent civil disobedience initiated by Mahatma Gandhi in India. It was a key event in the Indian independence movement.

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30. Which one of the following is the first enzyme to mix with food in the

Which one of the following is the first enzyme to mix with food in the digestive tract?

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Trypsin
Cellulose
Pepsin
Amylase
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Digestion begins in the mouth, where food is chewed and mixed with saliva. Saliva contains the enzyme salivary amylase (also known as ptyalin), which starts the enzymatic breakdown of carbohydrates (starch) into simpler sugars. Other enzymes listed, such as pepsin (in the stomach) and trypsin (in the small intestine), act later in the digestive tract. Cellulose is a type of carbohydrate, not a human digestive enzyme.
– The mouth is the beginning of the digestive tract where food mixes with saliva.
– Saliva contains salivary amylase (ptyalin).
– Salivary amylase starts the digestion of starch.
– Pepsin acts in the stomach, and trypsin acts in the small intestine.
Salivary amylase works best in a slightly alkaline to neutral pH (around 6.7 to 7.0) present in the mouth. Its activity is inhibited by the acidic environment of the stomach. Although carbohydrate digestion starts in the mouth, it is completed in the small intestine by pancreatic amylase.

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