UPSC NDA-1

1. Common salt (NaCl) is not used as a raw material for preparation of

Common salt (NaCl) is not used as a raw material for preparation of which one of the following compounds?

Bleaching powder
Baking soda
Plaster of Paris
Washing soda
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The correct answer is (C) Plaster of Paris.
Plaster of Paris (Calcium sulfate hemihydrate, CaSO4·½H2O) is produced by heating gypsum (Calcium sulfate dihydrate, CaSO4·2H2O) to about 150°C. The main raw material for Plaster of Paris is gypsum.
Common salt (NaCl) is a key raw material for the production of:
– Bleaching powder: Chlorine gas, used to make bleaching powder, is typically produced by electrolysis of brine (aqueous NaCl).
– Baking soda (NaHCO3) and Washing soda (Na2CO3): Both are primarily manufactured using the Solvay process, which utilizes brine (NaCl solution), ammonia, and carbon dioxide.
Thus, NaCl is a raw material (directly or indirectly) for bleaching powder, baking soda, and washing soda, but not for Plaster of Paris.

2. Mirage is an illustration of

Mirage is an illustration of

only dispersion of light.
only reflection of light.
only total internal reflection of light.
both refraction and total internal reflection of light.
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The correct answer is (D) both refraction and total internal reflection of light.
Mirages are atmospheric optical illusions caused by the bending of light (refraction) as it passes through layers of air with different temperatures and thus different refractive indices. Near hot surfaces (like roads or sand in deserts), the air is hotter and less dense than the air above, meaning its refractive index is lower. Light from the sky or distant objects travels downwards into these layers of increasingly rarer (hotter) air. It bends away from the normal. If the angle of incidence becomes greater than the critical angle at the boundary between two air layers, total internal reflection occurs. This reflected light travels upwards to the observer’s eye, creating the illusion of an image displaced from the actual object’s position.
Refraction is the initial bending of light through the varying density/temperature layers. Total internal reflection occurs when light traveling from a denser medium to a rarer medium hits the boundary at an angle greater than the critical angle, and all light is reflected back into the denser medium. Both processes are necessary for the formation of most common mirages (like inferior mirages).

3. If a ray of light enters from a rarer medium to a denser medium at zer

If a ray of light enters from a rarer medium to a denser medium at zero angle of incidence, it would

reflect back.
go straight.
turn towards right.
bend at 45°.
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The correct answer is (B) go straight.
When a ray of light is incident normally (at zero angle of incidence) on the boundary between two different media, it passes from one medium to the other without changing its direction, regardless of whether it is moving from a rarer to a denser medium or vice versa. The angle of incidence is the angle between the incident ray and the normal to the surface. If this angle is zero, the angle of refraction (the angle between the refracted ray and the normal) will also be zero, as predicted by Snell’s Law (n1 sinθ1 = n2 sinθ2).
Snell’s Law states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for a given pair of media. If θ1 = 0, then sinθ1 = 0. Thus, n2 sinθ2 = 0. Since n2 (refractive index of the second medium) is not zero, sinθ2 must be zero, which means θ2 = 0. Therefore, the refracted ray also lies along the normal, meaning it goes straight. Some partial reflection may occur at the boundary, but the transmitted light goes straight.

4. The major source of vitamins and minerals for vegetarians is

The major source of vitamins and minerals for vegetarians is

black gram and wheat.
rice and mustard.
vegetables and fruits.
soya bean and milk.
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The correct answer is (C) vegetables and fruits.
Vegetables and fruits are widely recognized as the most significant sources of a broad spectrum of vitamins, minerals, antioxidants, and dietary fiber for vegetarians and non-vegetarians alike. A varied intake of different types of vegetables and fruits ensures adequate supply of essential micronutrients.
While black gram, wheat, rice, mustard, soya bean, and milk provide various nutrients (protein, carbohydrates, some vitamins/minerals), they do not collectively offer the same wide variety and abundance of vitamins and minerals as a diverse diet rich in vegetables and fruits. Soya bean is excellent for protein, and milk for calcium and some vitamins (for lacto-vegetarians), but fruits and vegetables are fundamental for overall micronutrient intake.

5. If human blood is placed in a 2% detergent solution, what will happen

If human blood is placed in a 2% detergent solution, what will happen to the RBC?

The RBC will shrink.
The RBC will swell and become turgid.
The RBC will swell and burst.
The RBC will lyse.
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The correct answer is (D) The RBC will lyse.
Detergents are surfactants that disrupt cell membranes, which are primarily composed of lipid bilayers and proteins. Placing red blood cells (RBCs) in a detergent solution causes the detergent molecules to interact with and solubilize the lipids and proteins of the cell membrane. This disruption leads to the breakdown and disintegration of the cell membrane, a process called lysis.
While osmotic effects (swelling/bursting in hypotonic solutions or shrinking in hypertonic solutions) can cause RBCs to change shape and potentially lyse (in hypotonic conditions), the primary action of a detergent is direct chemical disruption of the membrane structure, leading to lysis regardless of simple osmosis. A 2% detergent solution is a potent cell lysing agent.

6. In a typical flower, germinating pollen grains pass through several pa

In a typical flower, germinating pollen grains pass through several parts of the gynoecium before they reach the ovule. A list of the parts of gynoecium is given below in different combinations. Choose the combination that represents the correct sequence of pollen tube pathway/journey :

Style, Stigma, Ovary
Stigma, Style, Ovary
Pistil, Stigma, Ovary
Ovary, Pistil, Style
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The correct answer is (B) Stigma, Style, Ovary.
In the typical process of fertilization in flowering plants, a pollen grain lands on the stigma (the receptive tip of the pistil/gynoecium). If compatible, the pollen grain germinates and grows a pollen tube. This pollen tube grows down through the style (the stalk connecting the stigma to the ovary) and eventually reaches the ovary, where it enters an ovule to deliver the male gametes. Thus, the correct sequence of the pollen tube pathway is Stigma -> Style -> Ovary.
The pistil or carpel is the entire female reproductive part of a flower, typically consisting of the stigma, style, and ovary. Starting the sequence with “Pistil” is not detailing the pathway *through* the parts of the gynoecium.

7. During seed germination, the part of the embryo which grows into root

During seed germination, the part of the embryo which grows into root is

Radicle.
Plumule.
Cotyledon.
Epicotyl.
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The correct answer is (A) Radicle.
During seed germination, the embryo within the seed develops into a seedling. The radicle is the embryonic root, which is the first part of the seedling to emerge from the seed during germination. It grows downwards into the soil to anchor the seedling and absorb water and nutrients.
The plumule is the embryonic shoot, which develops upwards into the stem and leaves. Cotyledons are seed leaves that store food or perform photosynthesis temporarily. The epicotyl is the part of the embryonic shoot above the cotyledons.

8. Which one of the following statements is true for a simple harmonic os

Which one of the following statements is true for a simple harmonic oscillator ?

Force acting is directly proportional to the displacement from the mean position and is in same direction.
Force acting is directly proportional to the displacement from the mean position and is in opposite direction.
Acceleration of the oscillator is constant.
The velocity of the oscillator is not periodic.
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The correct answer is (B) Force acting is directly proportional to the displacement from the mean position and is in opposite direction.
A simple harmonic oscillator (SHO) is defined by the condition that the restoring force acting on the oscillating body is directly proportional to its displacement from the equilibrium (mean) position and is always directed towards the equilibrium position. This is mathematically represented as F = -kx, where F is the force, x is the displacement, and k is the force constant. The negative sign indicates the force is in the opposite direction to the displacement.
Option A is incorrect because the force is in the opposite direction to the displacement (restoring force). Option C is incorrect because the acceleration (a = F/m = -kx/m) is proportional to the displacement and thus varies; it is not constant. Option D is incorrect because in SHM, the motion is periodic, meaning all properties like velocity, displacement, and acceleration repeat over time.

9. Light waves are incident on an air-glass boundary. Some of the light w

Light waves are incident on an air-glass boundary. Some of the light waves are reflected and some are refracted in the glass. Which one of the following properties is the same for the incident wave and the refracted wave?

Speed
Direction
Brightness
Frequency
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The correct answer is (D) Frequency.
When light waves pass from one medium to another (like air to glass), their speed and wavelength change, but their frequency remains constant. The frequency of a wave is determined by the source emitting the light and does not change when the medium changes.
Speed of light changes because the refractive index of the medium changes (speed = speed of light in vacuum / refractive index). Wavelength changes proportionally to the speed (speed = frequency * wavelength). Direction changes due to refraction (bending of light), unless the incidence is normal to the surface. Brightness (intensity) changes due to partial reflection at the boundary, absorption, and scattering within the medium.

10. ‘Beats’ is a phenomenon that occurs when frequencies of two harmonic w

‘Beats’ is a phenomenon that occurs when frequencies of two harmonic waves are

equal.
far apart.
multiples of each other.
nearly same.
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The correct answer is (D) nearly same.
‘Beats’ is a phenomenon that occurs when two waves of slightly different frequencies interfere with each other. This interference results in periodic variations in the intensity of the combined wave, heard as a waxing and waning of sound (or seen as flickering in light).
The beat frequency is the difference between the frequencies of the two individual waves (f_beat = |f1 – f2|). For distinct beats to be perceived, the frequency difference must be relatively small (typically less than about 7-10 Hz for sound waves). If the frequencies are exactly equal, they interfere constructively or destructively to produce a wave of constant amplitude. If the frequencies are far apart, the rapid variations in intensity are not perceived as beats.
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