#molecules

Applications of EM Waves in Communication and Medicine

Which type of electromagnetic waves are emitted by hot bodies and molecules?

**Radio waves** effective for long-distance communication because low frequency waves diffract around Earth curvature and reflect from ionosphere, enabling beyond line-of-sight, used in AM (≈10⁶ Hz) ground wave, short wave sky wave. Microwaves used for satellite due to high frequency penetrates ionosphere and directional beam. The document states that infrared waves are produced by hot bodies and molecules, often referred to as heat waves. Using c = fλ, E₀/B₀ = c, I_d = ε₀ dΦ_E/dt, and spectrum classification λ = c/f, evaluation yields Infrared waves, illustrating EM wave transverse nature and

Ref: NCERT > Physics Book > Electromagnetic Waves > Applications of EM Waves in Communication and Medicine

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Internal Energy of Ideal Gases

A gas occupies 33.6 litres at STP. How many molecules are present? (N_A = 6.02 × 10²³ mol⁻¹, molar volume at STP = 22.4

**Ideal gas internal energy** proportional to temperature, U = (f/2) R T per mole, monatomic 3/2 R T, diatomic 5/2 R T, change ΔU = f/2 n R ΔT, for temperature increase internal energy rises, explaining why heating gas at constant volume raises U entirely as heat. Number of moles (μ) = VolumeMolar volume = (33.6)/(22.4) = 1.5 mol.Number of molecules = μ × N_A = 1.5 × 6.02 × 10²³ = 9.03 × 10²³. Substituting values gives 9.03 × 10²³, which matches expected kinetic theory result, confirming mean free path λ = 1/(√2 n π d²), ideal gas law P V = n R

Ref: NCERT > Physics Book > Behaviour of Perfect Gas and Kinetic Theory > Internal Energy of Ideal Gases

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Gas Laws and Volume-Temperature Relations

A gas occupies a volume of 11.2 litres at STP. How many molecules are present in this gas? (N_A = 6.02 × 10²³ mol⁻¹)

**Gas laws** Boyle, Charles, Gay-Lussac are special cases of ideal gas equation, for constant pressure volume-temperature relation V ∝ T, for constant temperature pressure-volume inverse, for constant volume pressure-temperature direct, enabling calculation of new volume from temperature ratio. Molar volume at STP = 22.4 litres/mol.Number of moles (μ) = (11.2)/(22.4) = 0.5 mol .Number of molecules = μ × N_A = 0.5 × 6.02 × 10²³ = 3.01 × 10²³ . Substituting values gives 3.01 × 10²³, which matches expected kinetic theory result, confirming mean free path λ = 1/(√2 n π d²), ideal gas law P V = n R

Ref: NCERT > Physics Book > Behaviour of Perfect Gas and Kinetic Theory > Gas Laws and Volume-Temperature Relations

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Mean Free Path and Molecular Diameter

A gas occupies 67.2 litres at STP. How many molecules are present? (N_A = 6.02 × 10²³ mol⁻¹, molar volume at STP = 22.4

**Mean free path** λ = 1/(√2 n π d²) is average distance molecule travels between collisions, n number density (m⁻³), d molecular diameter (m), π≈3.14. Inversely proportional to n and d², larger n or d reduces λ. Rearranged d² = 1/(√2 n π λ), so d = √(1/(√2 n π λ)), enabling diameter estimation from measured λ and n. Number of moles (μ) = VolumeMolar volume = (67.2)/(22.4) = 3.0 mol.Number of molecules = μ × N_A = 3.0 × 6.02 × 10²³ = 1.806 × 10²⁴. Substituting values gives 1.806 × 10²⁴, which matches expected kinetic theory result, confirming mean free path λ =

Ref: NCERT > Physics Book > Behaviour of Perfect Gas and Kinetic Theory > Mean Free Path and Molecular Diameter

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CHEMISTRY

How many molecules are in 12 g of CH₃OH? (Molar mass = 32 g/mol, Avogadro number = 6.022 × 10²³)

Given: How many molecules are in 12 g of CH₃OH? (Molar mass = 32 g/mol, Avogadro number = 6.022 × 10²³) These values define the system as per NCERT data. Formula: Moles = 12 / 32 = 0.375 mol. This is the standard NCERT relation for this phenomenon. Substitution & Calculation: Molecules = 0.375 × 6.022 × 10²³ ≈ 2.258 × 10²³. Result: The computed value matches the expected outcome and confirms the correct choice. Units and powers like J kg⁻¹ K⁻¹, m/s², 10⁻⁵ are properly used as per NCERT.

Ref: NCERT Chemistry Textbook for Class XI and XII, Chapter: Some Basic Concepts, Structure of Atom and Periodicity, Topic: Mole concept, atomic models and periodic trends.

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CHEMISTRY

How many molecules are in 22 g of CO₂? (Molar mass = 44 g/mol, Avogadro number = 6.022 × 10²³)

Given: How many molecules are in 22 g of CO₂? (Molar mass = 44 g/mol, Avogadro number = 6.022 × 10²³) These values define the system as per NCERT data. Formula: Moles = 22 / 44 = 0.5 mol. This is the standard NCERT relation for this phenomenon. Substitution & Calculation: Molecules = 0.5 × 6.022 × 10²³ = 3.011 × 10²³. Result: The computed value matches the expected outcome and confirms the correct choice. Units and powers like J kg⁻¹ K⁻¹, m/s², 10⁻⁵ are properly used as per NCERT.

Ref: NCERT Chemistry Textbook for Class XI and XII, Chapter: Some Basic Concepts, Structure of Atom and Periodicity, Topic: Mole concept, atomic models and periodic trends.

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CHEMISTRY

How many molecules are in 4 g of H₂? (Molar mass = 2 g/mol, Avogadro number = 6.022 × 10²³)

Given: How many molecules are in 4 g of H₂? (Molar mass = 2 g/mol, Avogadro number = 6.022 × 10²³) These values define the system as per NCERT data. Formula: Moles = 4 / 2 = 2 mol. This is the standard NCERT relation for this phenomenon. Substitution & Calculation: Molecules = 2 × 6.022 × 10²³ = 1.2044 × 10²⁴. Result: The computed value matches the expected outcome and confirms the correct choice. Units and powers like J kg⁻¹ K⁻¹, m/s², 10⁻⁵ are properly used as per NCERT.

Ref: NCERT Chemistry Textbook for Class XI and XII, Chapter: Some Basic Concepts, Structure of Atom and Periodicity, Topic: Mole concept, atomic models and periodic trends.

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VSEPR Theory and Shapes of Molecules

Which molecule has a T-shaped molecular geometry?

In ClF₃ , chlorine is sp³d hybridized with 5 electron pairs (3 bonding, 2 lone), resulting in a T-shaped geometry.

Ref: NCERT Class 11 Chemistry > Chapter 4: Chemical Bonding and Molecular Structure > Topic: VSEPR Theory and Shapes of Molecules

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Chemiosmotic Hypothesis and Factors Affecting Photosynthesis

Which of the following molecules is directly involved in the light-dependent reactions?

NADP+ accepts electrons and hydrogen to form NADPH in the light-dependent reactions.

Ref: NCERT Class 11 Biology Chapter 11: Photosynthesis in Higher Plants Chemiosmotic Hypothesis and Factors Affecting Photosynthesis

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Acid, Base, pH

Which molecules are directly involved in translation?

mRNA, tRNA, rRNA is the accurate answer because it correctly identifies the biological function or role described in this question. In Acid, Base, pH, understanding the specific functions of molecules, enzymes, or structures is fundamental. mRNA, tRNA, rRNA fulfills this particular biological role through its specific structural properties, biochemical activity, or physiological mechanism. The other options (DNA, RNA, protein, DNA, rRNA, tRNA, and mRNA, snRNA, miRNA) serve different biological functions or are associated with other processes, pathways, or structural roles within the cell or or

Ref: Lehninger Principles of Biochemistry, Nelson & Cox, 8th Ed., Ch. 2

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Bioenergetics

Which of the following has the most negative ΔG°?

Hydrolysis of phosphoenolpyruvate (PEP) is the scientifically accurate answer to this question. Within the study of Bioenergetics, this concept is well-established through extensive research and is documented in standard scientific literature. The specific properties, mechanisms, or characteristics of Hydrolysis of phosphoenolpyruvate (PEP) directly address what is being asked. Among the other options, Hydrolysis of ATP, Hydrolysis of glucose, and Hydrolysis of pyruvate do not correctly answer this question because they either refer to different concepts, describe properties of other molecules

Ref: Campbell Biology, Urry et al., 12th Ed.

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