UPSC NDA-1

31. Equal volume of all gases, when measured at the same temperature and p

Equal volume of all gases, when measured at the same temperature and pressure, contain an equal number of particles. Who proposed the above law ?

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Charles
Boyle
Avogadro
Lussac
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The law stating that equal volumes of all gases, at the same temperature and pressure, contain the same number of molecules is known as Avogadro’s Law. It was proposed by Italian scientist Amedeo Avogadro in 1811. This law is a key principle in chemistry and relates the volume of a gas to the number of moles (and thus the number of particles) present.
Avogadro’s Law relates the volume of a gas to the number of particles (molecules or atoms) under constant temperature and pressure conditions.
Boyle’s Law relates pressure and volume (at constant temperature and number of particles). Charles’s Law relates volume and temperature (at constant pressure and number of particles). Gay-Lussac’s Law relates pressure and temperature (at constant volume and number of particles). These laws, along with Avogadro’s Law, combine to form the ideal gas law (PV = nRT).

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32. Copper sulphate crystals available in the market are blue coloured cry

Copper sulphate crystals available in the market are blue coloured crystals. By careful heating, they turn to white colour. Which one of the following is responsible for the blue colour ?

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Oxygen
Nitrogen
Water
Hydrogen
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Copper sulphate crystals available in the market are typically copper(II) sulphate pentahydrate (CuSO₄·5H₂O). The blue colour is due to the presence of water molecules coordinated to the copper ions in the crystal lattice. When heated, these crystals lose the water of crystallization, turning into anhydrous copper(II) sulphate (CuSO₄), which is white or off-white. The colour change is a classic demonstration of the role of water of crystallization.
The blue colour of hydrated copper sulphate is caused by the presence of water molecules bound within the crystal structure.
The process of heating hydrated copper sulphate to remove water is an example of dehydration. The reverse process, adding water to anhydrous copper sulphate, will restore the blue colour and is often used as a test for the presence of water. Other metal salts also form coloured hydrates where water of crystallization affects the colour.

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33. Which among the following is the correct arrangement of halogens in th

Which among the following is the correct arrangement of halogens in the increasing order of their oxidizing nature ?

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F, Cl, Br, I
Cl, Br, F, I
Br, I, Cl, F
I, Br, Cl, F
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The oxidizing nature of an element refers to its ability to gain electrons and cause the oxidation of another substance. For halogens (Group 17 elements: F, Cl, Br, I, At), the oxidizing power generally decreases down the group. This is because electronegativity and electron affinity decrease, while the atomic radius increases, making it less favorable to gain an electron as you move from Fluorine to Iodine. Therefore, the increasing order of their oxidizing nature is Iodine (I) < Bromine (Br) < Chlorine (Cl) < Fluorine (F). Fluorine is the strongest oxidizing agent among the halogens.
– Oxidizing nature is the ability to gain electrons.
– For halogens, oxidizing power decreases down the group (from F to I).
– This is due to decreasing electronegativity and electron affinity.
– The order of oxidizing strength is F₂ > Cl₂ > Br₂ > I₂.
– The increasing order of oxidizing nature is I < Br < Cl < F.
Fluorine is the most electronegative element and has a very high oxidizing potential. It can oxidize all other halide ions. Chlorine can oxidize bromide and iodide ions. Bromine can oxidize iodide ions, but not fluoride or chloride ions. Iodine is the weakest oxidizing agent among the common halogens.

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34. For manufacturing of glass, which among the following is used as a sou

For manufacturing of glass, which among the following is used as a source of silica ?

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Fine clay soil
Wood powder
Coconut shell
Sand
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Glass is primarily composed of silica (silicon dioxide, SiO₂). The main raw material used as a source of silica for glass manufacturing is sand, specifically high-purity silica sand (often called quartz sand). Other components like soda ash (sodium carbonate) and limestone (calcium carbonate) are added to lower the melting point and improve workability.
– Glass is mainly made of silica (SiO₂).
– The primary natural source of silica used in glass manufacturing is sand.
– High purity silica sand is preferred for glassmaking.
Fine clay soil contains silica, but it also contains many impurities (like alumina, iron oxides) that would affect the clarity and properties of the glass. Wood powder and coconut shells are organic materials and not sources of silica for glassmaking.

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35. Which among the following is the popular method for manufacture of amm

Which among the following is the popular method for manufacture of ammonia ?

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Ostwald's process
Haber-Bosch process
Electric furnace process
Electrolysis process
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The industrial manufacture of ammonia (NH₃) from nitrogen (N₂) and hydrogen (H₂) is achieved through the Haber-Bosch process. This process involves reacting nitrogen from the air with hydrogen, usually derived from natural gas, at high temperature (400-450°C) and high pressure (150-250 atm) over an iron catalyst.
– Ammonia (NH₃) is synthesized from N₂ and H₂.
– The industrial method is called the Haber-Bosch process.
– It uses high temperature, high pressure, and an iron catalyst.
Ostwald’s process is used for the industrial production of nitric acid (HNO₃) from ammonia. Electrolysis is a process used to decompose substances using electricity. Electric furnaces are used for melting metals and other high-temperature processes, but not specifically for the Haber-Bosch synthesis.

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36. Which among the following statements is not correct with respect to al

Which among the following statements is not correct with respect to allotropes of Carbon ?

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Graphite is a good conductor of electricity.
Diamond is the hardest substance known.
Fullerene is one of the allotropes of carbon.
Next to diamond, graphite is the second hardest known substance.
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Diamond is indeed the hardest naturally occurring substance known. Graphite, another allotrope of carbon, has a layered structure that allows the layers to slide over each other. This makes graphite very soft, greasy to touch, and suitable for use as a lubricant and in pencil leads. It is far from being the second hardest known substance; many materials, both natural and synthetic, are significantly harder than graphite.
– Allotropes are different structural modifications of an element.
– Diamond is the hardest known substance.
– Graphite is soft and used as a lubricant.
– Fullerene is an allotrope of carbon.
– Graphite’s soft nature contradicts the statement that it is the second hardest substance.
Other allotropes of carbon include carbon nanotubes, graphene, and amorphous carbon. The different properties of carbon allotropes arise from the different ways carbon atoms are bonded together in their structures.

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37. Which one of the following is the correct arrangement of metals in the

Which one of the following is the correct arrangement of metals in the decreasing order of their reactivity ?

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Iron, Sodium, Silver, Copper
Silver, Copper, Iron, Sodium
Sodium, Copper, Silver, Iron
Sodium, Iron, Copper, Silver
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The reactivity of metals decreases as you move down the reactivity series. The reactivity series ranks metals based on their tendency to lose electrons and undergo oxidation. A metal higher in the series can displace a metal lower in the series from its salt solution. The standard reactivity series places Sodium (Na) very high, followed by Iron (Fe), then Copper (Cu), and finally Silver (Ag) is quite low. Therefore, the decreasing order of reactivity is Sodium, Iron, Copper, Silver.
– Metals are ranked by their reactivity (tendency to lose electrons).
– The reactivity series is K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au > Pt.
– The metals in the options are Sodium (Na), Iron (Fe), Copper (Cu), Silver (Ag).
– Their order in the series is Na > Fe > Cu > Ag.
Highly reactive metals like Sodium react vigorously with cold water. Moderately reactive metals like Iron react with steam. Less reactive metals like Copper and Silver do not react with water or steam and are found uncombined in nature more often.

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38. What is the specific purpose of using potassium hydroxide during the s

What is the specific purpose of using potassium hydroxide during the saponification process ?

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To obtain soaps which are hard on the skin
To obtain soaps which are soft on the skin
To obtain natural fragrance
To make the saponification very economical
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Saponification is the process of hydrolyzing fats or oils using an alkali (strong base) to produce soap and glycerol. The type of alkali used influences the properties of the resulting soap. Sodium hydroxide (NaOH) typically yields hard soaps, suitable for bar soap. Potassium hydroxide (KOH) typically yields soft or liquid soaps, often used in liquid hand soap, shaving cream, or soft paste soaps. Therefore, potassium hydroxide is used to obtain soaps which are soft on the skin or in liquid form.
– Saponification uses a strong base to hydrolyze fats/oils.
– NaOH produces hard soaps.
– KOH produces soft or liquid soaps.
– The softness of the soap is desirable for certain applications like liquid soaps or those used on the skin.
Natural fragrances are added separately to the soap formulation and are not a result of using KOH specifically. While the cost of NaOH vs KOH can be a factor in manufacturing, the primary reason for choosing KOH is to achieve a softer soap consistency.

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39. Which one of the following statements about bryophytes is not correct

Which one of the following statements about bryophytes is not correct ?

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The plant body is a gametophyte.
They are also called the amphibians of plant kingdom.
The plant body is attached to the substratum by rhizoids.
Specialized water-conducting tissues are present.
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Bryophytes are non-vascular plants, which means they lack specialized vascular tissues like xylem and phloem for the efficient transport of water, minerals, and sugars over long distances. While they may have some rudimentary conducting cells, they do not possess the well-developed, specialized vascular tissues found in tracheophytes (ferns, gymnosperms, angiosperms).
– Bryophytes are non-vascular plants.
– They lack specialized water-conducting tissues (xylem) and nutrient-conducting tissues (phloem).
– The dominant phase of the life cycle is the gametophyte.
– They are often called amphibians of the plant kingdom because they require water for fertilization.
– They are anchored to the substratum by rhizoids.
The absence of true vascular tissues limits the size of bryophytes and their ability to colonize dry environments efficiently. Water absorption primarily occurs directly through the plant surface.

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40. Which one of the following is not a characteristic feature of fungi ?

Which one of the following is not a characteristic feature of fungi ?

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Cell wall is made of chitin
Filamentous mycelium is present
Can carry out photosynthesis
Asexual spores are produced
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Fungi are eukaryotic organisms that belong to their own kingdom. They are heterotrophs, meaning they obtain nutrients by absorbing organic matter from their environment. They lack chloroplasts and the necessary machinery for photosynthesis. Therefore, the ability to carry out photosynthesis is not a characteristic feature of fungi.
– Fungi are heterotrophic organisms.
– They lack chloroplasts.
– They cannot perform photosynthesis.
– Other listed options (cell wall of chitin, filamentous mycelium, asexual spores) are characteristic features of many fungi.
The cell wall of fungi is typically composed of chitin, a tough polysaccharide. Many fungi grow as a network of filamentous structures called hyphae, collectively forming a mycelium. Fungi reproduce asexually and/or sexually, often producing spores.

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