Chemistry

11. The main constituents of atmospheric air are Oxygen (O₂) and Nitrogen

The main constituents of atmospheric air are Oxygen (O₂) and Nitrogen (N₂). The composition of O₂ and N₂ is approximately :

29% and 70% respectively.
19% and 80% respectively.
21% and 78% respectively.
23% and 76% respectively.
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The Earth’s atmosphere is primarily a mixture of gases. The two most abundant gases in dry atmospheric air are Nitrogen (N₂) and Oxygen (O₂).
The approximate composition of dry atmospheric air by volume is:
Nitrogen (N₂) ≈ 78.09%
Oxygen (O₂) ≈ 20.95%
Argon (Ar) ≈ 0.93%
Carbon Dioxide (CO₂) ≈ 0.04%
Trace gases (Neon, Helium, Methane, Krypton, Hydrogen, etc.) make up the rest. Water vapor is also present, but its concentration varies significantly depending on location and weather. The question likely refers to dry air composition.

Looking at the options for the composition of O₂ and N₂:
A) 29% O₂, 70% N₂
B) 19% O₂, 80% N₂
C) 21% O₂, 78% N₂
D) 23% O₂, 76% N₂

Comparing these options to the actual percentages (≈20.95% O₂ and ≈78.09% N₂), option C (21% and 78%) is the closest approximation.

– Atmospheric air is a mixture of gases.
– The main constituents are Nitrogen (N₂) and Oxygen (O₂).
– Their approximate percentages by volume are about 78% Nitrogen and 21% Oxygen.
While Nitrogen and Oxygen make up the vast majority of the atmosphere (about 99%), the remaining 1% includes important gases like Argon, which is the third most abundant gas, and Carbon Dioxide, which plays a significant role in the greenhouse effect, despite its small concentration. These percentages can be taught as roughly 4/5th Nitrogen and 1/5th Oxygen for simplification, but 78% and 21% are more accurate approximate figures often cited.

12. Dyes in black ink can be separated by :

Dyes in black ink can be separated by :

evaporation.
centrifugation.
sublimation.
chromatography.
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Black ink is typically a mixture of several coloured dyes. To separate the different components (dyes) of a mixture, various separation techniques can be used. The technique suitable for separating different coloured dyes in ink is chromatography.
Chromatography is a technique used to separate mixtures based on the differential distribution of components between a stationary phase and a mobile phase. For separating dyes in ink, paper chromatography is a common method. The paper acts as the stationary phase, and a solvent (like water or alcohol) acts as the mobile phase. As the solvent moves up the paper by capillary action, it carries the different dyes with it. Dyes that are more soluble in the solvent and have weaker interactions with the paper move faster and further up the paper, resulting in their separation into distinct spots at different heights.

Let’s consider the other options:
A) Evaporation separates a soluble solid from a liquid solvent by heating the solution to evaporate the solvent. This would only leave the mixture of dyes behind, not separate them.
B) Centrifugation separates components of a mixture based on their density by spinning at high speed. It is used for separating solids from liquids or liquids of different densities (e.g., separating cream from milk, separating blood cells from plasma). It is not suitable for separating dissolved dyes.
C) Sublimation is the process where a substance changes directly from a solid to a gas state upon heating (e.g., dry ice, iodine). It is used to separate sublimable solids from non-sublimable ones. Dyes in ink are not typically sublimable.

– Black ink is a mixture of different coloured dyes.
– Chromatography is a separation technique used to separate components of a mixture based on their different affinities for a stationary phase and a mobile phase.
– Paper chromatography is specifically effective for separating different dyes in ink.
Paper chromatography is a simple and effective type of chromatography often demonstrated in schools. Other types include thin-layer chromatography (TLC), column chromatography, gas chromatography (GC), and high-performance liquid chromatography (HPLC), all based on the same principle of differential partitioning between phases.

13. Which one of the following metals is mixed with gold to provide streng

Which one of the following metals is mixed with gold to provide strength to the jewellery?

Manganese
Mica
Aluminium
Copper
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Pure gold (24 carat) is very soft and malleable, making it unsuitable for crafting durable jewellery. It is typically alloyed with other metals to increase its hardness and strength. Copper is a common metal used for this purpose, along with silver, nickel, and zinc.
– Alloying increases the durability and wear resistance of gold jewellery.
– The caratage of gold indicates the proportion of pure gold in the alloy (e.g., 18K gold is 75% gold).
The choice of alloying metal also affects the colour of the gold. For example, copper gives a reddish tint (rose gold), while silver and palladium create white gold.

14. Which one of the following is an example of low explosive?

Which one of the following is an example of low explosive?

Gunpowder
Gelatine
TNT
Dynamite
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Low explosives are substances that deflagrate (burn rapidly) rather than detonate (explode via a supersonic shockwave). Gunpowder (including black powder and smokeless powder) is a classic example of a low explosive. The burning speed creates a rapid expansion of gases, suitable for propellants (like in firearms or fireworks) but not for shattering effects required in demolition. Gelatine, TNT (Trinitrotoluene), and Dynamite are all high explosives used for their destructive detonating power.
Low explosives deflagrate, while high explosives detonate.
The primary difference lies in the speed of decomposition and the resulting pressure wave. High explosives decompose much faster, creating a shockwave that propagates at supersonic speeds, causing detonation. Low explosives burn comparatively slowly at subsonic speeds, causing deflagration.

15. Isotope of Cobalt is used in the treatment of

Isotope of Cobalt is used in the treatment of

Cancer.
Goitre.
Beriberi.
Crohn's disease.
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The radioactive isotope Cobalt-60 (⁶⁰Co) is widely used in medicine, particularly in radiotherapy for the treatment of cancer. It emits gamma rays which are used to kill cancer cells.
Isotopes are atoms of the same element with different numbers of neutrons.
Radioactive isotopes (radioisotopes) decay, emitting radiation.
⁶⁰Co is a common source of gamma rays for external beam radiotherapy machines (historically known as ‘cobalt bombs’).
While radiotherapy is a key use, ⁶⁰Co is also used for sterilization of medical equipment and food irradiation due to its potent gamma radiation. Goitre is often treated with Iodine-131.

16. When electricity is passed through brine, it produces

When electricity is passed through brine, it produces

NaCl
NaOH
KCl
KOH
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The electrolysis of brine (a concentrated aqueous solution of sodium chloride, NaCl) is an industrial process that produces sodium hydroxide (NaOH), chlorine gas (Cl₂), and hydrogen gas (H₂). The overall reaction is 2NaCl (aq) + 2H₂O (l) → 2NaOH (aq) + Cl₂ (g) + H₂ (g).
Brine is a solution of NaCl in water.
Electrolysis is the process of using electricity to drive a non-spontaneous chemical reaction.
The products are sodium hydroxide, chlorine, and hydrogen.
This process is known as the chlor-alkali process and is a major industrial method for producing these three important chemicals. NaOH is a strong base used in many industries, while Cl₂ is used for disinfection and manufacturing, and H₂ is used as a fuel or in chemical synthesis.

17. Chips bags contain which gas ?

Chips bags contain which gas ?

Oxygen
Hydrogen
Carbon dioxide
Nitrogen
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Chips bags are filled with nitrogen gas. Nitrogen is an inert gas that helps prevent oxidation of the chips, which causes them to become stale and rancid. It also provides cushioning, protecting the fragile chips from breaking during transport and handling.
Nitrogen gas is inert, meaning it does not react readily with the food.
Oxygen would react with the fats in the chips, causing rancidity.
The gas also helps maintain the structural integrity of the chips.
This process of flushing food packaging with an inert gas is called Modified Atmosphere Packaging (MAP) and is commonly used for various food products to extend shelf life.

18. Conversion of limestone to quick lime is an example of

Conversion of limestone to quick lime is an example of

decomposition reaction.
substitution reaction.
combination reaction.
double decomposition reaction.
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Limestone is primarily calcium carbonate (CaCO₃). Quick lime is calcium oxide (CaO). The conversion of limestone to quick lime involves heating calcium carbonate to a high temperature, which causes it to break down into calcium oxide and carbon dioxide gas: CaCO₃ (s) → CaO (s) + CO₂ (g). This reaction where a single compound breaks down into two or more simpler substances is called a decomposition reaction.
Decomposition reaction: A single reactant breaks down into simpler products.
Combination reaction: Two or more reactants combine to form a single product.
Substitution reaction: An atom or group is replaced by another atom or group.
Double decomposition reaction: Two compounds exchange ions or groups to form two new compounds.
This process, the thermal decomposition of calcium carbonate, is known as calcination or lime burning and is carried out in a kiln.

19. pH of blood is

pH of blood is

7·0
6·5
7·15
7·40
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The pH of healthy human blood is maintained within a narrow range of 7.35 to 7.45. This slightly alkaline range is crucial for proper metabolic function. Option D, 7.40, falls within this normal range and is often cited as an average value.
pH measures the acidity or alkalinity of a solution.
A pH of 7 is neutral. Below 7 is acidic, and above 7 is alkaline (basic).
Maintaining blood pH homeostasis is vital for physiological processes.
Deviations from the normal blood pH range can lead to serious health conditions such as acidosis (pH below 7.35) or alkalosis (pH above 7.45). The body has buffer systems to help maintain this narrow pH range.

20. Sodium chlorate is used in

Sodium chlorate is used in

textile printing and dyeing.
match industry.
antiseptics.
disinfectants.
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Sodium chlorate (NaClO₃) is a strong oxidizing agent. It is widely used in the textile industry as an oxidizing agent for dyeing and printing processes. It is also used in the production of chlorine dioxide, a bleaching agent.
Sodium chlorate is a chemical compound with the formula NaClO₃.
Its primary uses leverage its strong oxidizing properties.
Sodium chlorate is also used as a weedkiller, defoliant, and in some fireworks and explosives formulations, although potassium chlorate is more common in pyrotechnics.
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