UPSC CDS-1

41. What is the chemical composition of a soda-acid type fire

What is the chemical composition of a soda-acid type fire extinguisher?

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Solution of sodium hydrogen carbonate and sulfuric acid
Solution of sodium carbonate and sulfuric acid
Solution of carbon dioxide and sulfuric acid
Solution of sodium chloride and sulfuric acid
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UPSC CDS-1 – 2023
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A soda-acid fire extinguisher contains a solution of sodium hydrogen carbonate (NaHCO₃), also known as sodium bicarbonate or baking soda, and a separate container of sulfuric acid (H₂SO₄). When the extinguisher is activated, the acid mixes with the sodium bicarbonate solution. A chemical reaction occurs:
$2NaHCO_3 (aq) + H_2SO_4 (aq) \rightarrow Na_2SO_4 (aq) + 2H_2O (l) + 2CO_2 (g)$
This reaction produces a large volume of carbon dioxide gas (CO₂), which is expelled under pressure. The CO₂ gas is denser than air and blankets the fire, displacing oxygen and suppressing the combustion.
– Soda-acid fire extinguishers utilize the reaction between sodium hydrogen carbonate and sulfuric acid.
– The extinguishing agent is primarily carbon dioxide gas produced by the reaction.
Soda-acid extinguishers are effective on Class A fires (ordinary combustibles like wood, paper, textiles). They are not suitable for Class B (flammable liquids) or Class C (electrical) fires, and can be dangerous to use on electrical fires due to the water content. Modern fire extinguishers use different agents like foam, dry chemical powder, or CO₂ itself.

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42. A car moving with a speed of 12 m/s is subjected to brakes which produ

A car moving with a speed of 12 m/s is subjected to brakes which produces a deceleration of 6 m/s2. The car takes 2 s to stop after the application of brakes. What is the distance covered by the car after the application of brakes?

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12 m
24 m
36 m
48 m
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UPSC CDS-1 – 2023
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Given:
Initial velocity, $u = 12$ m/s
Deceleration, $a = -6$ m/s² (negative because it’s deceleration)
Final velocity, $v = 0$ m/s (the car stops)
Time, $t = 2$ s
We need to find the distance covered, $s$.
We can use the equation of motion $s = ut + (1/2)at^2$.
Substituting the given values:
$s = (12 \, \text{m/s}) \times (2 \, \text{s}) + (1/2) \times (-6 \, \text{m/s}^2) \times (2 \, \text{s})^2$
$s = 24 \, \text{m} + (1/2) \times (-6) \times 4 \, \text{m}$
$s = 24 \, \text{m} – (3) \times 4 \, \text{m}$
$s = 24 \, \text{m} – 12 \, \text{m}$
$s = 12 \, \text{m}$
Alternatively, using $v^2 = u^2 + 2as$:
$0^2 = (12)^2 + 2 \times (-6) \times s$
$0 = 144 – 12s$
$12s = 144$
$s = 144 / 12 = 12$ m.
– Use the appropriate kinematic equations for uniformly accelerated motion.
– Deceleration is negative acceleration.
The kinematic equations for constant acceleration are:
1. $v = u + at$
2. $s = ut + (1/2)at^2$
3. $v^2 = u^2 + 2as$
4. $s = (u+v)t/2$
These equations are valid only when acceleration is constant.

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43. Sound and light waves are

Sound and light waves are

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respectively longitudinal and transverse in air
respectively transverse and longitudinal in air
both longitudinal in air
both transverse in air
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Sound waves are mechanical waves that require a medium (like air, water, or solids) to propagate. In air, sound waves are longitudinal waves, meaning the particles of the medium vibrate back and forth parallel to the direction in which the wave travels, creating regions of compression and rarefaction.
Light waves are electromagnetic waves and do not require a medium to propagate (they can travel through a vacuum). Light waves are transverse waves, meaning the oscillations of the electric and magnetic fields are perpendicular to the direction in which the wave travels.
Therefore, sound waves are longitudinal in air, and light waves are transverse in air (and other media, or vacuum).
– Sound waves are longitudinal in gases and liquids.
– Light waves are always transverse.
While sound waves are longitudinal in air and fluids, they can be both longitudinal and transverse in solids. Other examples of transverse waves include waves on a string and some seismic waves (S-waves). Examples of longitudinal waves include P-waves (a type of seismic wave) and waves in a spring compressed and stretched along its length.

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44. The hydrogen bomb and the uranium bomb are based, respectively on

The hydrogen bomb and the uranium bomb are based, respectively on

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nuclear fusion and fission
fission and thermonuclear fusion
geothermal fission and fusion
geothermal fusion and fission
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The hydrogen bomb, also known as a thermonuclear bomb, is based on the principle of nuclear fusion. Nuclear fusion is a reaction in which two or more atomic nuclei collide at very high speeds and fuse to form a new, heavier nucleus, releasing a large amount of energy. This reaction typically requires extremely high temperatures, hence “thermonuclear”.
The uranium bomb, or atomic bomb (specifically a fission bomb), is based on the principle of nuclear fission. Nuclear fission is a nuclear reaction in which a heavy nucleus, such as an isotope of uranium or plutonium, splits into lighter nuclei, releasing a large amount of energy.
– Hydrogen bomb uses nuclear fusion.
– Uranium bomb uses nuclear fission.
– Both processes release enormous amounts of energy, but fusion generally releases more energy per unit mass than fission.
Fission bombs are used to ignite fusion reactions in hydrogen bombs, providing the necessary high temperatures and pressures. Nuclear power plants also use controlled nuclear fission reactions to generate electricity.

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45. The r.m.s. potential difference between the red live wire and black ne

The r.m.s. potential difference between the red live wire and black neutral wire in Indian domestic electric supply is

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160 V
220 V
300 V
410 V
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UPSC CDS-1 – 2023
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The standard r.m.s. (root mean square) voltage for domestic electric supply in India is 220 volts. This is the effective voltage that determines the power delivered to electrical appliances. The peak voltage is higher, approximately $220 \times \sqrt{2} \approx 311$ volts.
– The voltage of AC power is usually specified by its r.m.s. value.
– The standard domestic supply voltage in India is 220-240 V AC at 50 Hz.
Different countries use different standard voltages and frequencies for domestic power supply (e.g., 120 V at 60 Hz in North America, 230 V at 50 Hz in much of Europe). The red wire is typically the live or phase wire, and the black wire is the neutral wire. The potential difference exists between the live and neutral wires.

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46. Three resistors of resistances 11 $\Omega$, 22 $\Omega$ and 33 $\Omega

Three resistors of resistances 11 $\Omega$, 22 $\Omega$ and 33 $\Omega$ are connected in parallel. Their equivalent resistance is equal to

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66 $Omega$
22 $Omega$
12 $Omega$
6 $Omega$
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UPSC CDS-1 – 2023
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The equivalent resistance ($R_{eq}$) of resistors connected in parallel is given by the formula:
$1/R_{eq} = 1/R_1 + 1/R_2 + 1/R_3 + …$
Given resistances are $R_1 = 11 \, \Omega$, $R_2 = 22 \, \Omega$, and $R_3 = 33 \, \Omega$.
$1/R_{eq} = 1/11 + 1/22 + 1/33$
To add these fractions, find a common denominator, which is 66.
$1/R_{eq} = (6 \times 1)/(6 \times 11) + (3 \times 1)/(3 \times 22) + (2 \times 1)/(2 \times 33)$
$1/R_{eq} = 6/66 + 3/66 + 2/66$
$1/R_{eq} = (6 + 3 + 2) / 66 = 11 / 66$
$R_{eq} = 66 / 11 = 6 \, \Omega$.
– For resistors in parallel, the reciprocal of the equivalent resistance is the sum of the reciprocals of individual resistances.
– The equivalent resistance in a parallel circuit is always less than the smallest individual resistance. In this case, 6 $\Omega$ is less than 11 $\Omega$.
Resistors can be connected in two main ways: series and parallel. In a series connection, resistances add up ($R_{eq} = R_1 + R_2 + R_3 + …$). In a parallel connection, the voltage across each resistor is the same, and the total current is the sum of currents through each resistor.

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47. Xylem is a type of complex tissue in plants for upward conduction of w

Xylem is a type of complex tissue in plants for upward conduction of water. Which one of the following xylem tissues consists of living cells?

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Tracheid
Vessel
Xylem parenchyma
Xylem fibre
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UPSC CDS-1 – 2023
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Xylem is composed of four main types of elements: tracheids, vessels, xylem parenchyma, and xylem fibres. Among these, only xylem parenchyma cells are living cells.
Tracheids and vessels are the main water-conducting elements and are dead, hollow tubes at maturity. Xylem fibres are typically dead and provide mechanical support. Xylem parenchyma cells are involved in storage of food materials (starch, fats) and lateral conduction of water and minerals.
Phloem, another complex plant tissue, is responsible for the translocation of sugars and also contains living cells, such as sieve elements and companion cells.

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48. In grasses, intercalary meristem is usually located at

In grasses, intercalary meristem is usually located at

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root tip
lateral sides of stem
base of leaves
shoot tip
This question was previously asked in
UPSC CDS-1 – 2023
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Intercalary meristems are located at the base of internodes or leaves in monocotyledonous plants like grasses. They are derived from apical meristems and are situated between mature tissues.
The presence of intercalary meristems allows grasses to regrow quickly after being grazed or cut, as they contribute to the elongation of stems and leaves from points other than the tips.
Apical meristems (at root and shoot tips) are responsible for primary growth (increase in length). Lateral meristems (like vascular cambium and cork cambium) are responsible for secondary growth (increase in thickness).

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49. In plant cells, RNA is present in

In plant cells, RNA is present in

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cytoplasm only
nuclei and cytoplasm only
nuclei, cytoplasm, mitochondria, chloroplast and endoplasmic reticulum
nuclei, cytoplasm, mitochondria, chloroplast and ribosomes
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In plant cells, RNA is found in various locations: the nucleus (where transcription occurs and various RNAs are synthesized and processed), the cytoplasm (containing mRNA, tRNA, rRNA, and free ribosomes), mitochondria (with their own genetic material and protein synthesis machinery, including rRNA and tRNA), chloroplasts (similarly having their own genetic material and protein synthesis machinery, including rRNA and tRNA), and ribosomes (which are themselves composed of rRNA and proteins, and are the sites of protein synthesis using mRNA and tRNA).
RNA’s presence in mitochondria and chloroplasts reflects their endosymbiotic origin and semi-autonomous nature, possessing their own genetic systems.
Endoplasmic Reticulum (ER) is involved in protein synthesis via ribosomes attached to its surface (RER), but RNA itself is not considered a component of the ER membrane or lumen; it is associated with the ribosomes on the ER.

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50. Which one of the following is essential for thyroid gland to make

Which one of the following is essential for thyroid gland to make thyroxin?

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NaCl
KCl
Cholesterol
Iodine
This question was previously asked in
UPSC CDS-1 – 2023
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Iodine is an essential trace element required by the thyroid gland to synthesize thyroid hormones, namely thyroxine (T4) and triiodothyronine (T3).
Iodine atoms are incorporated into the structure of the thyroxine and triiodothyronine molecules. Deficiency of iodine can lead to impaired thyroid hormone production, resulting in conditions like goiter and hypothyroidism.
The thyroid gland actively accumulates iodide ions from the blood. The synthesis of thyroid hormones involves the iodination of tyrosine residues on the protein thyroglobulin.

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