Chemistry Archives

151. Which one among the following fertilizers is a source of nitrogen ?

Which one among the following fertilizers is a source of nitrogen ?

[amp_mcq option1=”Superphosphate” option2=”Potassium sulfate” option3=”Bone meal” option4=”Urea” correct=”option4″]

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Urea, with the chemical formula (NH₂)₂CO, is a widely used nitrogenous fertilizer. It contains a high percentage of nitrogen by weight. When applied to soil, urea is hydrolyzed by enzymes to produce ammonia (NH₃), which is then converted to ammonium ions (NH₄⁺) and nitrate ions (NO₃⁻) that plants can absorb as sources of nitrogen. Superphosphate is a phosphorus fertilizer, potassium sulfate is a potassium fertilizer, and bone meal is primarily a source of phosphorus and calcium.

Plants require macronutrients like nitrogen (N), phosphorus (P), and potassium (K) for growth. Fertilizers provide these nutrients. Nitrogen fertilizers specifically supply nitrogen compounds to the soil.

Urea is an organic compound and is often considered the most important nitrogen fertilizer globally due to its high nitrogen content and ease of synthesis. Other common nitrogen fertilizers include ammonium nitrate (NH₄NO₃) and ammonium sulfate ((NH₄)₂SO₄).

152. Which one among the following is an example of oxidation reaction ?

Which one among the following is an example of oxidation reaction ?

[amp_mcq option1=”Freezing of water” option2=”Dissolving sugar in water” option3=”Rusting of iron” option4=”Boiling of petrol” correct=”option3″]

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Oxidation is a chemical reaction where a substance loses electrons or its oxidation state increases. Rusting of iron is the process where iron reacts with oxygen and water to form hydrated iron(III) oxides, commonly known as rust. This is a chemical change where iron is oxidized from its elemental state (oxidation state 0) to an oxidation state of +3 in the iron oxides. Freezing of water, dissolving sugar, and boiling of petrol are physical changes or processes, not chemical reactions involving oxidation in the typical sense tested in such questions.

An oxidation reaction involves the loss of electrons or an increase in oxidation state. Chemical changes result in the formation of new substances. Physical changes alter the form or appearance but not the chemical composition.

Rusting is a specific type of corrosion, which is an electrochemical process. The chemical equation for the formation of rust is complex, but the overall process involves the oxidation of iron: Fe → Fe³⁺ + 3e⁻, and the reduction of oxygen.

153. Which one among the following has valency of 3 ?

Which one among the following has valency of 3 ?

[amp_mcq option1=”Carbon” option2=”Oxygen” option3=”Nitrogen” option4=”Sodium” correct=”option3″]

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Nitrogen commonly has a valency of 3, particularly in compounds like ammonia (NH3).

– Valency is the measure of the combining capacity of an element. It is typically equal to the number of electrons an atom gains, loses, or shares to achieve a stable electron configuration (usually a full outermost electron shell).
– Carbon (Atomic number 6): Electron configuration is 2, 4. It needs 4 electrons to complete its outer shell, so its common valency is 4 (e.g., CH4, CO2).
– Oxygen (Atomic number 8): Electron configuration is 2, 6. It needs 2 electrons, so its common valency is 2 (e.g., H2O, O2).
– Nitrogen (Atomic number 7): Electron configuration is 2, 5. It needs 3 electrons to complete its outer shell. Thus, its common valency is 3 (e.g., NH3, NCl3). Nitrogen can also exhibit other valencies (e.g., +5 in nitrates), but 3 is a very common valency.
– Sodium (Atomic number 11): Electron configuration is 2, 8, 1. It tends to lose 1 electron to achieve a stable configuration. Its valency is 1 (e.g., NaCl, Na2O).

The concept of valency is simplified and primarily applies to covalent bonding and simple ionic compounds. More rigorous descriptions of bonding use oxidation states and formal charges, especially for elements in higher periods or in complex compounds. However, for basic elements like N, O, C, and Na, their typical valencies are characteristic.

154. What is the maximum number of electrons that can occupy the first shel

What is the maximum number of electrons that can occupy the first shell of an atom ?

[amp_mcq option1=”2″ option2=”4″ option3=”8″ option4=”16″ correct=”option1″]

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The maximum number of electrons that can occupy the first electron shell of an atom is 2.

– Electron shells (also called energy levels) surround the nucleus of an atom. They are denoted by the principal quantum number, n (n=1, 2, 3, …), where n=1 is the shell closest to the nucleus.
– The maximum number of electrons that can occupy a given shell is determined by the formula 2n², where n is the shell number.
– For the first shell (n=1), the maximum number of electrons is 2 * (1)² = 2 * 1 = 2.
– For the second shell (n=2), the maximum number of electrons is 2 * (2)² = 2 * 4 = 8.
– For the third shell (n=3), the maximum number of electrons is 2 * (3)² = 2 * 9 = 18, and so on.

The first shell (n=1) contains only one subshell, the ‘s’ subshell, which can hold a maximum of 2 electrons. The electron configuration follows the Aufbau principle, Hund’s rule, and the Pauli exclusion principle, filling lower energy levels before higher ones.

155. Which one among the following is commonly used as an ‘anti-skinning ag

Which one among the following is commonly used as an ‘anti-skinning agent’ in paints ?

[amp_mcq option1=”Gelatin” option2=”N-methyl pyrrolidone” option3=”Pyridine” option4=”Polyhydroxy phenol” correct=”option4″]

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The correct answer is D) Polyhydroxy phenol.

‘Skinning’ in paints refers to the formation of a solid or semi-solid film on the surface of the liquid paint when exposed to air. This is primarily due to the oxidation and subsequent polymerization of the drying oils or alkyd resins used as binders, catalyzed by metal driers. Anti-skinning agents are added to paints to prevent this surface oxidation and polymerization. Many anti-skinning agents are volatile antioxidants or complexing agents that temporarily deactivate the metal driers. Phenolic compounds, particularly polyhydroxy phenols and hindered phenols, are effective antioxidants that can scavenge free radicals and prevent the oxidation chain reactions that lead to skinning. Oximes (like methyl ethyl ketoxime) are also commonly used as anti-skinning agents by complexing with metal driers. Polyhydroxy phenol represents a class of compounds known for their antioxidant properties, making them suitable for use as anti-skinning agents.

Gelatin is a protein used as a gelling agent, thickener, or binder. N-methyl pyrrolidone (NMP) is a strong polar solvent. Pyridine is a basic organic compound often used as a solvent or catalyst. None of these are primarily used as anti-skinning agents in paints, unlike phenolic compounds or oximes.

156. The chemical reaction: 2AgCl (s) → 2Ag (s) + Cl₂ (g) takes place

The chemical reaction:
2AgCl (s) → 2Ag (s) + Cl₂ (g)
takes place

[amp_mcq option1=”in dark” option2=”in sunlight” option3=”on heating” option4=”under high pressure” correct=”option2″]

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The correct answer is B) in sunlight.

The chemical reaction shown, 2AgCl (s) → 2Ag (s) + Cl₂ (g), is the decomposition of silver chloride into silver and chlorine gas. Silver halides like silver chloride (AgCl) and silver bromide (AgBr) are known to be sensitive to light. This decomposition reaction is catalyzed by light, particularly sunlight or bright artificial light. This property is fundamental to traditional black and white photography where silver halides in photographic film undergo decomposition upon exposure to light, forming a latent image.

This type of decomposition reaction, which occurs in the presence of light, is called a photolytic decomposition reaction. While some decomposition reactions occur on heating (thermolysis), the decomposition of silver chloride is prominently triggered by light energy. Dark conditions prevent this reaction. High pressure would likely favour the solid reactant over the gaseous product, not cause decomposition.

157. The mass of 0.5 mole of N₂ gas is

The mass of 0.5 mole of N₂ gas is

[amp_mcq option1=”7 g” option2=”14 g” option3=”21 g” option4=”28 g” correct=”option2″]

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The correct answer is B) 14 g.

The mass of a substance can be calculated using the number of moles and its molar mass. The formula is: Mass = Number of moles × Molar mass.
Nitrogen gas is diatomic, represented as N₂. The atomic mass of Nitrogen (N) is approximately 14 g/mol. Therefore, the molar mass of N₂ gas is 2 × 14 g/mol = 28 g/mol.
Given the number of moles is 0.5 mole, the mass of 0.5 mole of N₂ gas is 0.5 mol × 28 g/mol = 14 g.

A mole is a unit of amount of substance, defined as containing Avogadro’s number (approximately 6.022 × 10²³) of elementary entities (atoms, molecules, ions, etc.). The molar mass of a substance is the mass of one mole of that substance.

158. Which of the following anions has a valency of –3 ?

Which of the following anions has a valency of –3 ?

[amp_mcq option1=”Nitride” option2=”Nitrate” option3=”Sulphide” option4=”Sulphate” correct=”option1″]

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The correct answer is A) Nitride.

Valency, in the context of ions, refers to the magnitude of the charge on the ion. An anion is a negatively charged ion.
– Nitride is the anion formed from a nitrogen atom gaining electrons to achieve a stable electron configuration. Nitrogen is in Group 15 and typically gains 3 electrons to form N³⁻. Thus, the valency of the nitride ion is -3.
– Nitrate is the polyatomic anion NO₃⁻, with an overall charge of -1.
– Sulphide is the anion formed from a sulphur atom gaining electrons. Sulphur is in Group 16 and typically gains 2 electrons to form S²⁻. The valency of the sulphide ion is -2.
– Sulphate is the polyatomic anion SO₄²⁻, with an overall charge of -2.

The charge on the ion directly corresponds to its valency (with the sign indicating whether it’s a cation or anion). Therefore, the anion with a valency of -3 is Nitride (N³⁻).

159. Which one among the following elements is polyatomic ?

Which one among the following elements is polyatomic ?

[amp_mcq option1=”Phosphorus” option2=”Sulphur” option3=”Chlorine” option4=”Aluminium” correct=”option2″]

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The correct answer is B) Sulphur.

An element is considered polyatomic if its stable molecular form consists of more than two atoms of that element bonded together. Sulphur exists in various allotropes, the most common and stable form being the S₈ molecule, which has a ring structure containing eight sulphur atoms. This makes sulphur a polyatomic element.

Chlorine exists as diatomic molecules (Cl₂). Aluminium is a metal and exists as individual atoms in its elemental state (monatomic in solid form). Phosphorus exists in various allotropes, such as white phosphorus (P₄, tetratomic) and red phosphorus (polymeric). While Phosphorus (P₄) is also polyatomic, Sulphur (S₈) is a common example used to illustrate polyatomic elements in chemistry, and it is explicitly polyatomic in its stable form. Given the options and the need for a single correct answer, S₈ is a clear example of a polyatomic molecule.

160. The intermixing of particles of two different types of matter on their

The intermixing of particles of two different types of matter on their own is called

[amp_mcq option1=”Osmosis” option2=”Brownian motion” option3=”Diffusion” option4=”Conductance” correct=”option3″]

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The correct answer is C) Diffusion.

Diffusion is the net movement of anything generally from a region of higher concentration to a region of lower concentration. This movement is driven by the random motion of particles (molecules or atoms) leading to their spontaneous intermixing until the concentration is uniform throughout. The intermixing of particles of two different types of matter on their own is the definition of diffusion.

Osmosis is a specific type of diffusion involving the movement of solvent molecules (usually water) across a semipermeable membrane from a region of high solvent concentration to a region of low solvent concentration. Brownian motion is the random movement of microscopic particles suspended in a liquid or gas, caused by collisions with the molecules of the surrounding medium; it is the underlying cause of diffusion but not the intermixing process itself. Conductance refers to the ability of a material to conduct electricity.