Question 1

An ideal gas is expanded from (p1, V1, T1) to (p2, V2, T2) under different conditions. The correct statement(s) among the following is(are)

Accepted Answer

When an ideal gas expands under different conditions, the relationship between the pressure, volume, and temperature changes according to the ideal gas law. Here's the explanation for the possible statements: Use the Ideal Gas Law: The ideal gas law is given by: pV = nRT, where: p = pressure of the gas V = volume of the gas n = number of moles of the gas R = universal gas constant T = temperature of the gas (in Kelvin) Is the gas undergoing isothermal expansion? If the gas expands isothermally, the temperature remains constant (T1 = T2). In this case, according to the ideal gas law, p1V1 = p2V2 because T1 = T2. This means that the pressure decreases when the volume increases, and vice versa, for an isothermal expansion. Is the gas undergoing adiabatic expansion? If the gas expands adiabatically (no heat exchange), the relationship between pressure, volume, and temperature is governed by the adiabatic equation: pV^γ = constant, where γ is the heat capacity ratio (Cp/Cv). In this case, both pressure and temperature decrease as the volume increases, and this is a faster change than in an isothermal process. Is the gas undergoing isobaric or isochoric expansion? If the gas is expanded at constant pressure (isobaric process), the temperature and volume change proportionally according to pV = nRT, so V1/T1 = V2/T2. If the gas is expanded at constant volume (isochoric process), the pressure and temperature change proportionally, following p1/T1 = p2/T2. Final Considerations: The type of process (isothermal, adiabatic, isobaric, or isochoric) dictates the relationship between pressure, volume, and temperature during the expansion. Final answer: The correct statement(s) would depend on the specific conditions of the gas expansion (whether it is isothermal, adiabatic, isobaric, or isochoric). Each process has its own governing equations.

Question 2

Bohr model (standing waves): The number of de Broglie wavelengths (waves) that fit in the electron's orbit for the n^th Bohr orbit equals what? Use Bohr–de Broglie quantization: circumference = nλ. Choose the correct expression.

Accepted Answer

Given data Bohr's condition: angular momentum quantization implies standing waves. Concept/Approach For a stable orbit, the circumference satisfies 2πr = nλ which means exactly n wavelengths fit around the orbit. Final Answer n

Question 3

Metals (optical property): The luster (shiny appearance) of a metal is primarily due to what? Focus on fundamental electronic structure of metals. Choose the correct cause.

Accepted Answer

Concept/Approach Metals have a sea of delocalized (free) electrons that reflect incident light efficiently, producing characteristic metallic luster. Final Answer Presence of free electrons

Question 4

Flames (Bunsen/gas): The hottest part of a gas flame is known as which zone? Consider a properly adjusted Bunsen burner flame. Choose the correct zone.

Accepted Answer

Concept/Approach With adequate air supply, a Bunsen flame is blue and non-luminous. The outer blue (non-luminous) zone is the hottest due to complete combustion. Note Some texts say “non-luminous outer zone” as the hottest; in a practical gas flame this is the blue zone. Final Answer Blue zone

Question 5

Reactivity (halogens): The very high chemical reactivity of fluorine is mainly due to what factor? Consider periodic trends and bond energetics. Choose the best reason.

Accepted Answer

Concept/Approach Fluorine has the highest electronegativity and very high electron affinity, driving strong oxidizing power. Its small size also contributes, but the principal textbook reason cited is electronegativity. Options (c) and (d) are incorrect: fluorine lacks accessible d-orbitals and the F–F bond is relatively weak, not strong. Final Answer Its high electronegativity

Question 6

Carbon allotropy (materials science): Which is the hardest allotropic form of carbon known for extreme hardness and abrasion resistance? Identify the correct carbon allotrope noted for its tetrahedral network and highest Mohs hardness. Choose the co…

Accepted Answer

Given data Asked: the hardest allotropic form of carbon. Concept/Approach Carbon occurs in several allotropes (diamond, graphite, amorphous carbon such as charcoal/coke). Diamond has a 3D network of sp3-hybridized carbon atoms, giving it the highest hardness. Why others are wrong • Graphite is soft and lubricating (layered sp2 sheets).• Charcoal and coke are amorphous and much softer. Final Answer Diamond

Question 7

Human physiology (nutrition): What is the principal physiological role of common salt (sodium chloride) in the diet related to digestion? Consider the function of chloride ions in gastric juice formation and normal digestive processes. Choose the co…

Accepted Answer

Given data Asked: the main physiological use of dietary salt in digestion. Concept/Approach Dietary NaCl supplies chloride ions, which parietal cells use to form hydrochloric acid (HCl) in gastric juice. HCl activates pepsinogen to pepsin and maintains acidic pH for protein digestion. Eliminate distractors • Taste/cooking/solubility are secondary or irrelevant to the physiological role in digestion. Final Answer Produce, in small amounts, the hydrochloric acid required for digestion

Question 8

Industrial chemistry (vanaspati): Which gas is used to manufacture vanaspati (hydrogenated vegetable oil) from vegetable oils? Identify the gaseous reactant used during catalytic hydrogenation of unsaturated oils. Choose the correct option.

Accepted Answer

Given data Process: converting vegetable oil to vanaspati by catalytic hydrogenation. Concept/Approach Unsaturated C=C bonds in oils are hydrogenated using hydrogen gas in presence of catalysts (e.g., Ni), producing semi-solid fat (vanaspati). Final Answer Hydrogen

Question 9

History of chemistry (classification of elements): Newlands, Mendeleev, and Meyer are associated with which foundational development? Recognize the contribution of these scientists to organizing elements and predicting properties. Choose the correct…

Accepted Answer

Given data Names: Newlands, Mendeleev, Lothar Meyer. Concept/Approach They developed early periodic classifications (Newlands' Law of Octaves; Mendeleev's periodic table with predictions; Meyer's atomic volume periodicity), leading to the modern periodic table. Final Answer The periodic table

Question 10

Natural products chemistry (essential oils): The key flavor constituent of cardamom oil is which compound? Identify the predominant component responsible for the characteristic aroma and flavor of cardamom. Choose the correct option.

Accepted Answer

Given data Main flavor compound sought in cardamom oil. Concept/Approach Cardamom oil contains significant 1,8-cineole (eucalyptol) and other terpenes; cineole is classically cited for the characteristic flavor. Final Answer Cineole

Question 11

Chemical bonding (valency): What is the maximum number of covalent bonds nitrogen can form? Consider valence-shell capacity for nitrogen (period 2) and typical compounds like ammonium. Choose the correct option.

Accepted Answer

Given data Nitrogen: Z = 7, valence shell 2s22p3. Concept/Approach In neutral covalent compounds (e.g., NH3) nitrogen forms three covalent bonds; however, its maximum covalency is four, as in NH4+, where N forms three normal covalent bonds and one dative (coordinate) covalent bond, totaling four covalent bonds. Note As a second-period element (no d-orbitals), nitrogen's maximum covalency is limited to 4. Final Answer 4

Question 12

Mole concept (Avogadro application): How many water molecules are present in a drop of water of volume 0.0018 mL at room temperature? Use density ≈ 1 g/mL and molar mass of water = 18 g/mol for the calculation. Choose the correct value.

Accepted Answer

Given data Volume = 0.0018 mL; ρ(H2O) ≈ 1 g/mL; M(H2O) = 18 g/mol; NA = 6.023 × 1023 mol−1. Step-by-Step calculation Mass = 0.0018 mL × 1 g/mL = 0.0018 gMoles = 0.0018 g ÷ 18 g/mol = 1.0 × 10−4 molNumber of molecules = 1.0 × 10−4 × 6.023 × 1023 = 6.023 × 1019 Common pitfalls Mixing up milliliters and liters or forgetting that density is ~1 g/mL for water at room temperature. Final Answer 6.023 × 10^19

Question 13

Atmospheric science (ozone layer): Which gas in the stratosphere filters the sun's ultraviolet radiation and protects living organisms from radiation damage? Identify the protective stratospheric constituent. Choose the correct option.

Accepted Answer

Concept/Approach The ozone layer in the stratosphere absorbs a significant portion of biologically harmful UV-B and UV-C radiation, shielding life on Earth. Final Answer Ozone

Question 14

Atomic structure (nucleus): The nucleus of an atom is composed of which fundamental particles? Recall the composition of the atomic nucleus versus the electron cloud. Choose the correct option.

Accepted Answer

Concept/Approach The atomic nucleus contains protons (+) and neutrons (0). Electrons (−) occupy the surrounding orbitals/cloud, not the nucleus. Final Answer Protons and neutrons

Question 15

Industrial catalysis (hydrogenation): Which metal is commonly used as a catalyst in the hydrogenation of oils to fats? Identify the standard heterogeneous catalyst employed in edible oil hydrogenation. Choose the correct option.

Accepted Answer

Concept/Approach Finely divided nickel (Ni) is the classic, economical hydrogenation catalyst for converting unsaturated oils to fats. Although Pt can catalyze hydrogenation, industrial vanaspati processes rely on Ni. Final Answer Ni

Question 16

Organic reaction type (oxime formation): The reaction of an aldehyde with hydroxylamine (e.g., CH3CHO + NH2OH → oxime + H2O) exemplifies which reaction class? Recognize the formation of an oxime with loss of water. Choose the correct option.

Accepted Answer

Given data General reaction: R–CHO + NH2OH → R–CH=N–OH (oxime) + H2O. Concept/Approach The reaction produces a single product (oxime) with elimination of water, a hallmark of a condensation reaction (specifically, condensation of carbonyl with hydroxylamine). Final Answer A condensation reaction

Question 17

Mineralogy (carbonates): Which mineral contains both magnesium and calcium in its composition? Identify the double carbonate featuring Ca and Mg. Choose the correct option.

Accepted Answer

Concept/Approach Dolomite is CaMg(CO3)2, a double carbonate of calcium and magnesium. Magnesite is MgCO3; Calcite is CaCO3; Carnallite is KMgCl3·6H2O. Final Answer Dolomite

Question 18

Nuclear engineering (moderation): In a nuclear reactor, graphite rods serve which primary function in the chain reaction? Focus on the role of graphite in neutron energy control. Choose the correct option.

Accepted Answer

Concept/Approach Graphite is a moderator. It slows fast neutrons to thermal energies, increasing the probability of fission in certain fuels (e.g., U-235). It neither produces neutrons nor reacts chemically to trigger fission. Final Answer Convert fast neutrons into thermal neutrons (moderator)

Question 19

Kinetic theory (molecular speeds): At the stated temperatures, molecules of which gas have the highest average speed? Use proportionality v ∝ √(T/M) comparing temperature (K) and molar mass. Choose the correct option.

Accepted Answer

Given data Speed ∝ √(T/M) (T in kelvin; M in g·mol−1). Calculations H₂ at −73°C ⇒ T = 200 K, M = 2 ⇒ T/M = 100CH₄ at 300 K ⇒ M = 16 ⇒ T/M = 18.75N₂ at 1,027°C ⇒ T = 1300 K, M = 28 ⇒ T/M ≈ 46.4O₂ at 0°C ⇒ T = 273 K, M = 32 ⇒ T/M ≈ 8.53Highest T/M ⇒ highest speed: H₂ at −73°C. Final Answer H₂ at −73°C

Question 20

Stoichiometry (counting in molecules): How many gram-moles of oxygen are present in 6.02 × 10²⁴ molecules of CO? Clarify whether you are counting oxygen as atoms present within CO molecules. Choose the correct value.

Accepted Answer

Given data & assumption 6.02 × 1024 CO molecules contain the same number of oxygen atoms. Older phrasing often uses 'gram-molecule' loosely; here we interpret it as moles of oxygen atoms present. Step-by-Step Moles of CO molecules = (6.02 × 1024)/(6.02 × 1023) = 10 molEach CO has 1 O atom ⇒ Moles of O atoms = 10 mol Alternative note If the question had asked for O₂ molecules, then 10 mol of O atoms correspond to 5 mol of O₂. But as worded (oxygen present in CO), the count refers to oxygen atoms = 10 mol. Final Answer 10 gram-molecule

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