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CHEMISTRY

This category covers chemistry questions across physical, organic and inorganic topics, from atomic structure and bonding to reactions, equations and periodic trends. Use it to practise problem solving or to revisit concepts that need reinforcing. Answers are provided so you can check your working and follow the reasoning.

45 questions

CHEMISTRY

What is the number of unpaired electrons in [Cr(Hâ‚‚O)6]^{3+ ?

Given: What is the number of unpaired electrons in [Cr(H₂O)6]^{3+ ? These values define the system as per NCERT data. Formula: Cr³⁺ ( d³ ) with H₂O in an octahedral field has 3 unpaired electrons ( t_{2g³ ), as it’s a d³ system.. This is the standard NCERT relation for this phenomenon. Substitution & Calculation: Substituting values like 1.2 × 10⁻⁵, 236 J kg⁻¹ K⁻¹, CH₃CH₂NH₂ etc. into the formula and simplifying step by step. 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 optical isomers are possible for [Cr(Câ‚‚Oâ‚„)3]^{3- ?

[Cr(Câ‚‚Oâ‚„)3]^{3- is octahedral with three bidentate oxalate ligands, lacking symmetry, and forms two optical isomers (d and l enantiomers). This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.

Ref: NCERT Chemistry Textbook for Class XI and XII, Chapter: Relevant Chemistry topic covering principles and examples as per NCERT.

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CHEMISTRY

A solution contains 10 mL of ethanol ( Câ‚‚Hâ‚…OH ) and 90 mL of water, with a total volume of 95 mL. What is the volume

Given: A solution contains 10 mL of ethanol ( C₂H₅OH ) and 90 mL of water, with a total volume of 95 mL. What is the volume percentage of ethanol? (Density of ethanol = 0.789 g/mL) These values define the system as per NCERT data. Formula: Volume % = fracVolume of ethanolTotal volume × 100. This is the standard NCERT relation for this phenomenon. Substitution & Calculation: Given volume of ethanol = 10 mL, total volume = 95 mL. Volume % = 10/95 × 100 = 10.53% . 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: Solutions, Topic: Concentration terms and colligative properties.

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CHEMISTRY

What is the mass percentage of potassium in KMnOâ‚„? (Atomic masses: K = 39, Mn = 55, O = 16)

Given: What is the mass percentage of potassium in KMnO₄? (Atomic masses: K = 39, Mn = 55, O = 16) These values define the system as per NCERT data. Formula: Molar mass = 39 + 55 + (4 × 16) = 39 + 55 + 64 = 158 g/mol. This is the standard NCERT relation for this phenomenon. Substitution & Calculation: Mass of K = 39 g. % K = (39 / 158) × 100 ≈ 24.68%. 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: Relevant Chemistry topic covering principles and examples as per NCERT.

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CHEMISTRY

What is the mass percentage of oxygen in K₂Cr₂O₇? (Atomic masses: K = 39, Cr = 52, O = 16)

Given: What is the mass percentage of oxygen in K₂Cr₂O₇? (Atomic masses: K = 39, Cr = 52, O = 16) These values define the system as per NCERT data. Formula: Molar mass = (2 × 39) + (2 × 52) + (7 × 16) = 78 + 104 + 112 = 294 g/mol. This is the standard NCERT relation for this phenomenon. Substitution & Calculation: Mass of O = 112 g. % O = (112 / 294) × 100 ≈ 38.1%. 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: Relevant Chemistry topic covering principles and examples as per NCERT.

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CHEMISTRY

A solution of 2.44 g of acetic acid ( CH₃COOH ) in 100 g of benzene shows a freezing point depression of 0.5 K. If the

Given: A solution of 2.44 g of acetic acid ( CH₃COOH ) in 100 g of benzene shows a freezing point depression of 0.5 K. If the molar mass is 60 g/mol, what is the van't Hoff factor due to dimerization? ( K_f = 5.12 K kg/mol ) These values define the system as per NCERT data. Formula: Molality = 2.44 / 60/0.1 = 0.4067 mol/kg. This is the standard NCERT relation for this phenomenon. Substitution & Calculation: Normal Δ T_f = 5.12 × 0.4067 = 2.08 K . Observed Δ T_f = 0.5 K . i = 0.5/2.08 = 0.24 . 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: Solutions, Topic: Concentration terms and colligative properties.

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CHEMISTRY

The number of moles of I^- oxidized by 1 mole of KMnOâ‚„ in acidic medium to form Iâ‚‚ is:

Given: The number of moles of I^- oxidized by 1 mole of KMnO₄ in acidic medium to form I₂ is: These values define the system as per NCERT data. Formula: 1 mole KMnO₄ oxidizes 5 moles I^- (10/2 = 5).. This is the standard NCERT relation for this phenomenon. Substitution & Calculation: 2MnO₄^- + 16H^+ + 10I^- -> 2Mn^{2+ + 8H₂O + 5I₂ . 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

The K_a of HClO is 3.0 × 10⁻⁸. What is the pH of a 0.01 M solution?

Given: The K_a of HClO is 3.0 × 10⁻⁸. What is the pH of a 0.01 M solution? These values define the system as per NCERT data. Formula: K_a = x²/0.01, 3.0 × 10⁻⁸= x²/0.01, x² = 3.0 × 10⁻¹⁰. This is the standard NCERT relation for this phenomenon. Substitution & Calculation: x = sqrt3.0 × 10⁻¹⁰ approx 5.48 × 10⁻⁵, pH = -log(5.48 × 10⁻⁵) approx 4.26 . 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: Solutions, Topic: Concentration terms and colligative properties.

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CHEMISTRY

What is the total number of valence electrons available for bonding in the CO molecule?

Carbon has 4 valence electrons ( 2s² 2p² ), and oxygen has 6 ( 2s² 2p⁴ ). Total = 4 + 6 = 10. This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.

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

The rate constant of a reaction is 1.2 × 10⁻⁴ s^{-1 at 320 K and 4.8 × 10⁻⁴ s^{-1 at 330 K. What is the activa

Given: The rate constant of a reaction is 1.2 × 10⁻⁴ s^{-1 at 320 K and 4.8 × 10⁻⁴ s^{-1 at 330 K. What is the activation energy in kJ mol^{-1 ? (R = 8.314 J/mol · K) These values define the system as per NCERT data. Formula: log k_2/k_1 = E_a/2.303R ( T_2 - T_1/T_1 T_2 ). This is the standard NCERT relation for this phenomenon. Substitution & Calculation: log frac4.8 × 10⁻⁴¹.2 × 10⁻⁴= log 4 = 0.602 . 0.602 = E_a/2.303 × 8.314 ( 10/320 × 330 ), E_a approx 64.7 kJ mol^{-1 . 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: Relevant Chemistry topic covering principles and examples as per NCERT.

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CHEMISTRY

Which of the following amines has the highest number of alkyl groups attached to nitrogen?

Triethylamine ( (CH₃CH₂)3N ) is a tertiary amine with three alkyl groups (ethyl) attached to nitrogen, the highest among the options. This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.

Ref: NCERT Chemistry Textbook for Class XI and XII, Chapter: Relevant Chemistry topic covering principles and examples as per NCERT.

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