Chemistry

261. Which one of the following gases gives acidic solution on dissolving i

Which one of the following gases gives acidic solution on dissolving in water?

[amp_mcq option1=”Hydrogen” option2=”Carbondioxide” option3=”Nitrogen” option4=”Oxygen” correct=”option2″]

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When carbon dioxide (CO₂) dissolves in water (H₂O), it reacts to form carbonic acid (H₂CO₃) through a reversible reaction: CO₂ + H₂O ⇌ H₂CO₃. Carbonic acid is a weak acid that can dissociate into hydrogen ions (H⁺) and bicarbonate ions (HCO₃⁻), and further into hydrogen ions and carbonate ions (CO₃²⁻). The presence of hydrogen ions increases the acidity of the solution.
Non-metal oxides that react with water form acidic solutions. CO₂ is an oxide of carbon, a non-metal. Other examples include SO₂ and NO₂, which form sulfurous/sulfuric acid and nitrous/nitric acid respectively, contributing to acid rain.
Hydrogen (H₂), Nitrogen (N₂), and Oxygen (O₂) are diatomic gases that do not react with water to form acids under normal conditions. H₂ is neutral. N₂ and O₂ are relatively inert. Oxides of metals, on the other hand, typically form alkaline solutions when dissolved in water (e.g., Na₂O + H₂O → 2NaOH).

262. If one mixes up ashes with animal fat, the substance received in the c

If one mixes up ashes with animal fat, the substance received in the crude form is called

[amp_mcq option1=”Pheromone” option2=”Soap” option3=”Cement” option4=”Concrete” correct=”option2″]

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The correct answer is B) Soap. Historically, soap was produced by boiling animal fat with lye, which is an alkaline solution obtained from leaching ashes (often wood ashes containing potassium carbonate, which reacts with water to form potassium hydroxide, or using lime to convert sodium carbonate from plant ashes into sodium hydroxide). The process, called saponification, involves the hydrolysis of fats or oils (triglycerides) by an alkali to produce glycerol and fatty acid salts, which are soap. Mixing ashes (source of alkali) with animal fat is a crude method of making soap.
– Soap is made through saponification, a reaction between fats/oils and an alkali.
– Animal fat provides triglycerides.
– Ashes, particularly from wood, can provide alkali (potassium carbonate/hydroxide) when mixed with water.
– This historical process yields crude soap.
– Pheromones are chemical signals released by organisms.
– Cement is a binder substance used in construction.
– Concrete is a composite material made from cement, aggregate, water, and sometimes admixtures.

263. Emulsion is known as a

Emulsion is known as a

[amp_mcq option1=”colloidal solution of substances having different physical states” option2=”true solution” option3=”distillation mixture for making alcohols” option4=”colloidal solution of two liquids” correct=”option4″]

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The correct answer is D) colloidal solution of two liquids. An emulsion is a specific type of colloid where one liquid is dispersed throughout another liquid in the form of tiny droplets. The two liquids are typically immiscible or poorly miscible.
– Emulsions are colloidal systems.
– The dispersed phase and the dispersion medium are both liquids.
– Examples include milk (fat droplets dispersed in water) and mayonnaise (oil dispersed in vinegar).
– Colloidal solutions can involve different physical states (e.g., solid in gas for smoke, liquid in gas for fog), but an emulsion is specifically liquid in liquid.
– A true solution is a homogeneous mixture where the solute is dissolved at the molecular or ionic level, unlike a colloid which has larger dispersed particles.
– Distillation is a separation technique, not a type of solution or mixture in this context.

264. The setting time of cement is lowered by adding

The setting time of cement is lowered by adding

[amp_mcq option1=”oxides of aluminium” option2=”gypsum” option3=”oxides of magnesium” option4=”silica” correct=”option1″]

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The correct answer is A) oxides of aluminium. The question asks what is added to lower the setting time of cement, which means making it set faster. Gypsum (option B) is added to *increase* the setting time (retard setting). While standard accelerators are typically calcium chloride or alkali aluminates, reactive forms of aluminium oxides or phases rich in alumina like Calcium Aluminate Cements (CAC) or specific additives containing activated alumina can act as accelerators, causing rapid setting. Therefore, among the given options, oxides of aluminium (in a suitable form or context as present in cement phases like C₃A) are the most plausible candidates for contributing to or accelerating the setting process compared to the other options which are either retarders (gypsum) or primary components/cause of expansion (magnesium oxide).
– Setting time refers to the time required for cement paste to lose its plasticity.
– Additives are used to control setting time: accelerators decrease setting time, retarders increase it.
– Gypsum is a common retarder, preventing flash set by reacting with C₃A.
– Oxides of aluminium are present in cement clinker primarily as tricalcium aluminate (C₃A), which hydrates rapidly and contributes to early setting. Certain forms of reactive alumina can act as accelerators.
– Calcium chloride (CaCl₂) is a very common and effective accelerator used in cement.
– Oxides of magnesium (MgO), if present in excess in portland cement, can cause delayed expansion and soundness issues, not primarily affecting initial setting time in a controlled manner.
– Silica (SiO₂) is a main component of cement (silicates C₃S and C₂S), which are responsible for strength development, but adding pure silica is not a method to control setting time.
– The phrasing “lowered by adding” implies acceleration. While gypsum is a crucial additive related to setting time, its effect is the opposite (increasing/retarding). This points towards A as the intended answer, assuming a context where an aluminium oxide based additive is used for acceleration.

265. The LPG cooking gas contains propane and butane as the constituents. A

The LPG cooking gas contains propane and butane as the constituents. A sulfur containing compound is added to the LPG, because

[amp_mcq option1=”it lowers the cost of production” option2=”it enhances the efficiency of LPG” option3=”it facilitates easy detection of leakage of the gas” option4=”it assists in liquefying hydrocarbons” correct=”option3″]

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The addition of a sulfur-containing compound to LPG cooking gas facilitates the easy detection of leakage.
LPG (Liquefied Petroleum Gas), which primarily consists of propane and butane, is naturally odorless. Leaked gas can accumulate and pose a significant fire and explosion hazard if not detected. To ensure safety, a strong-smelling substance, usually a volatile organic sulfur compound like ethyl mercaptan (ethanethiol), is added as an odorant. This allows even small leaks to be detected by smell, prompting corrective action before a dangerous concentration of gas builds up.
The amount of odorant added is very small, typically only a few parts per million, which is sufficient to make the gas detectable by the human nose at concentrations well below the flammability limit. The odorant does not affect the combustion properties or efficiency of the LPG.

266. When one strikes a safety match, the first step is

When one strikes a safety match, the first step is

[amp_mcq option1=”burning of sulfur” option2=”decomposition of potassium chlorate into potassium chloride and oxygen” option3=”conversion of a small amount of red phosphorus into white phosphorus” option4=”burning of glue and starch” correct=”option3″]

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When one strikes a safety match, the first step (after generating friction) is the conversion of a small amount of red phosphorus into white phosphorus.
A safety match head contains oxidizer (like KClO₃), fuel (sulfur), and binder. The striking surface contains red phosphorus, glass powder, and binder. Striking the head against the surface creates friction, which generates heat. This heat energy is sufficient to convert a tiny amount of red phosphorus on the strip into the highly reactive white phosphorus, which ignites instantly in air. This initial ignition then provides the heat to decompose the potassium chlorate in the match head, releasing oxygen, which oxidizes the sulfur, causing the main flame.
Burning of sulfur (A), decomposition of potassium chlorate (B), and burning of glue/starch (D – part of the binder) are subsequent steps that occur after the initial ignition triggered by the red phosphorus/white phosphorus conversion.

267. Which one of the following statements is correct ?

Which one of the following statements is correct ?

[amp_mcq option1=”Covalent bonds are directional” option2=”Ionic bonds are directional” option3=”Both covalent and ionic bonds are directional” option4=”Both covalent and ionic bonds are non-directional” correct=”option1″]

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Covalent bonds are directional.
Covalent bonds involve the sharing of electrons between specific atoms, leading to electron density concentrated in defined regions (orbitals) oriented in space. This directional nature of covalent bonds determines the geometry and shape of molecules, including bond angles and lengths.
Ionic bonds are formed by the electrostatic attraction between oppositely charged ions. This attraction is isotropic and extends in all directions equally around the ion. Thus, ionic bonds are non-directional, leading to the formation of extended crystal lattices rather than discrete molecules with fixed shapes determined by bond angles.

268. Which one of the following species is not capable of showing dispropor

Which one of the following species is not capable of showing disproportionation reaction ?

[amp_mcq option1=”ClO⁻” option2=”ClO₂⁻” option3=”ClO₃⁻” option4=”ClO₄⁻” correct=”option4″]

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ClO₄⁻ (Perchlorate) is not capable of showing disproportionation reaction.
Disproportionation is a redox reaction where an element in a specific oxidation state is simultaneously oxidized to a higher oxidation state and reduced to a lower oxidation state. For this to happen, the element must be in an intermediate oxidation state. In ClO₄⁻, Chlorine is in its highest common oxidation state of +7. It can only be reduced to a lower state (e.g., +5, +3, +1, 0, -1), but it cannot be oxidized further. Therefore, it cannot undergo disproportionation.
In ClO⁻ (+1), ClO₂⁻ (+3), and ClO₃⁻ (+5), Chlorine is in intermediate oxidation states and can be both oxidized and reduced, hence capable of disproportionation.

269. 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 :

List I
(Element)		List II
(Highest Valency)
A. Sulfur1. Five
B. Phosphorous2. Six
C. Lead3. Two
D. Silver4. Four

Code :

ABCD
(a)2413
(b)2143
(c)3142
(d)3412

[amp_mcq option1=”2, 4, 1, 3″ option2=”2, 1, 4, 3″ option3=”3, 1, 4, 2″ option4=”3, 4, 1, 2″ correct=”option2″]

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The correct match is A-2, B-1, C-4, D-3.
The highest common valency (or oxidation state) for the elements are:
– Sulfur (S): Can exhibit +6 (e.g., in sulfates), so highest valency is Six (2).
– Phosphorus (P): Can exhibit +5 (e.g., in phosphates), so highest valency is Five (1).
– Lead (Pb): Can exhibit +4 (e.g., PbO₂), so highest valency is Four (4).
– Silver (Ag): The most common valency/oxidation state is +1. While higher, unstable oxidation states exist, +1 is the standard. The option provides ‘Two’ (3) as the highest valency for Silver. Assuming this option set is intended, the pairings match option B for A, B, and C.
Based on standard chemistry, the highest common valency for Silver is 1. However, matching the provided options, A-2, B-1, C-4 align with common understanding, leading to option B being the most probable intended answer despite the inaccuracy regarding Silver’s listed highest valency.

270. Combination of one volume of nitrogen with three volumes of hydrogen

Combination of one volume of nitrogen with three volumes of hydrogen produces

[amp_mcq option1=”one volume of ammonia” option2=”two volumes of ammonia” option3=”three volumes of ammonia” option4=”one and a half volumes of ammonia” correct=”option2″]

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The reaction between nitrogen and hydrogen to produce ammonia is represented by the balanced chemical equation: N₂(g) + 3H₂(g) → 2NH₃(g). According to Avogadro’s law, at the same temperature and pressure, the ratio of the volumes of reacting gases and gaseous products is equal to the ratio of their stoichiometric coefficients in the balanced equation. Thus, 1 volume of nitrogen reacts with 3 volumes of hydrogen to produce 2 volumes of ammonia.
– The balanced equation for the Haber process is N₂(g) + 3H₂(g) → 2NH₃(g).
– The stoichiometric coefficients are 1 for N₂, 3 for H₂, and 2 for NH₃.
– At constant temperature and pressure, the volume ratio of reacting gases and gaseous products is equal to the mole ratio (and stoichiometric coefficient ratio).
This principle relating volumes of reacting gases to their stoichiometric coefficients is known as Gay-Lussac’s law of combining volumes.
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