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Elementary Ideas about the Structure of Atom Questions

Chapter: Atomic Structure & Laws | Total Available: 23 Real Questions

Question 1 of 10 Authentic UPSC NDA Question

The mass number of argon is 40. Which one ofthe following statements is correct?

Step-by-Step Logic & Solution

Correct Answer

✓ Option (b) is correct. The number of neutrons in argon is 18.

📖 Governing Law / Core Concept

The atomic number of an element indicates the number of protons, while the mass number is the total number of protons and neutrons in the nucleus. For argon (Ar), we have the following definitions:

Atomic number (Z) = Number of protons

Mass number (A) = Number of protons (p) + Number of neutrons (n)

For argon:

Mass number (\(A\)) = 40

Atomic number (\(Z\)) = 18

🧪 Step-by-Step Breakdown

\[ \begin{aligned} & A = p + n \\ & 40 = 18 + n \\ & n = 40 - 18 \\ & n = 22 \end{aligned} \]

Thus, argon has 22 neutrons. Since argon is neutral, the number of electrons also equals the number of protons, confirming there are 18 electrons.

🔍 Option Analysis

  • Option A: Incorrect. The number of protons in argon is 18, not 22.
  • Option B: Correct. The number of neutrons in argon is 22, calculated as shown.
  • Option C: Incorrect. The number of electrons is 18, equal to the number of protons.
  • Option D: Incorrect. The sum of protons and electrons is 36, not 40.

⚡ Mnemonic / Speed-Run

Remember: "Argon is neutral, argon is great, with 18 protons (as a plate)!" This helps recall that with 18 protons, neutrons add to 22 to make 40.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class 11 Chemistry, Chapter 2 (Structure of Atom).

Question 2 of 10 Authentic UPSC NDA Question

Which one of the following findings is NOT observed in Rutherford’s Nuclear Model of Atom?

Step-by-Step Logic & Solution
✓

1. Correct Answer

Option A is correct. Rutherford’s Nuclear Model of Atom did not propose the presence of a neutral center in the atom, such as a nucleus.

📖 Short Explanation

Rutherford’s Nuclear Model revolutionized atomic theory by introducing the existence of a small, dense nucleus, but it did not suggest the nucleus was neutral.

💡 3. Why Correct Answer is Correct

Rutherford’s model showed that the atom is mostly empty space with electrons orbiting a positively charged nucleus. The nucleus, which is very small and dense, contains most of the atom's mass. Rutherford concluded this through his famous gold foil experiment. While the nucleus was thought to consist of protons (positive charge), the notion of a neutral component within it (neutrons) was not introduced until later by James Chadwick in 1932.

❌ 4. Why Other Options are Wrong

  • •Option B: Correct as Rutherford’s model does indicate that nearly all the mass of the atom resides in the nucleus.
  • •Option C: Correct because the model depicts electrons revolving around the nucleus in circular paths.
  • •Option D: Correct as it reflects the fact that the size of the nucleus is very small compared to the rest of the atom.
⚡

NDA Speed-Run / Mnemonic Shortcut

Remember that Rutherford's atom model introduced the nucleus and its positive charge without detailing the presence of neutrons which are neutral.

🎯

5. Key Learning Point

Rutherford's experiment identified a nucleus filled with protons; it did not account for neutrons.

6. Visual Suggestion

A diagram showing a compact nucleus at the center with electrons orbiting in elliptical paths and differential sizes between the nucleus and the atom as a whole.

Question 3 of 10 Authentic UPSC NDA Question

Which one of the following conclusions could not be derived from Rutherfords -particle scattering experiment?

Step-by-Step Logic & Solution

Correct Answer

✓ Option (c) is correct. Electrons do not move in fixed energy orbits according to Rutherford's model.

📖 Governing Law / Core Concept

The foundational concept from Rutherford's experiment illustrates that atoms consist primarily of empty space, with most mass concentrated in a dense nucleus.

🧪 Step-by-Step Breakdown

Rutherford's gold foil experiment revealed several key points:

  • Most of the atom's volume is empty.
  • The nucleus is significantly smaller than the atom (radius ratio: ~105).
  • Rutherford did not propose a model for electron orbits, which was later introduced by Bohr.

Thus, the statement regarding fixed energy orbits for electrons could not be derived from his findings.

🔍 Option Analysis

  • A: Correctly states the atom's empty space.
  • B: Accurate ratio derived from the nucleus's size.
  • D: Correctly identifies that most atomic mass is nuclear.
  • C: Incorrect inference as stationary orbits were not a part of Rutherford's conclusions.

⚡ Mnemonic / Speed-Run

Remember: "Empty Nucleus Relates (E.N.R.)" to recall key findings of Rutherford's model (empty space, nucleus mass concentration).

6. Visual Suggestion

6. Visual Suggestion

A diagram illustrating the Rutherford experiment setup, indicating the alpha particle beam, gold foil, and deflection angles, would clarify the conclusions drawn from the experiment.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class XI Chemistry, Chapter 2 (Structure of Atom).

Question 4 of 10 Authentic UPSC NDA Question

Rutherfords alpha-particle  scattering experiment was responsible for the discovery of which one of the following?

Step-by-Step Logic & Solution

Correct Answer

✓ Option C is correct. Rutherford's experiment led to the discovery of the atomic nucleus.

📖 Governing Law / Core Concept

The atomic nucleus is the central component of an atom that contains protons and neutrons, comprising most of an atom's mass.

🧪 Step-by-Step Breakdown

Rutherford's alpha-particle scattering experiment involved directing alpha particles onto a thin gold foil. The key observations were:

  • A majority of the alpha particles passed through the foil, indicating that atoms are mostly empty space.
  • A small fraction were deflected at large angles, suggesting the presence of a dense, positively charged nucleus.

🔍 Option Analysis

A: Electron - Discovered by J.J. Thomson in 1897, these are negatively charged subatomic particles.

B: Proton - Identified by Ernest Rutherford in 1919, protons are positively charged particles found in the nucleus.

D: Neutron - Discovered by James Chadwick in 1932, neutrons are neutral particles also located in the nucleus.

⚡ Mnemonic / Speed-Run

Remember "Rutherford Rebuilt Atom" to recall that Rutherford's experiment redefined atomic structure with the nucleus at its core.

6. Visual Suggestion

6. Visual Suggestion

A diagram of Rutherford's gold foil experiment showing the paths of alpha particles, illustrating how most pass through while a few are deflected at sharp angles, highlighting the nucleus's presence.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class XI Chemistry, Chapter 2 (Structure of Atom).

Question 5 of 10 Authentic UPSC NDA Question

What is the maximum number of electrons in the M-Shell?

Step-by-Step Logic & Solution

Correct Answer

✓ Option C is correct. The M-Shell can accommodate a maximum of 18 electrons.

📖 Governing Law / Core Concept

The maximum number of electrons in a shell is given by the formula \(2n^2\), where \(n\) is the principal quantum number.

🧪 Step-by-Step Breakdown

In this case, for the M-Shell:

\[ n = 3 \quad (\text{M-Shell}) \]

Substituting into the formula:

\[ \text{Maximum Electrons} = 2n^2 = 2(3^2) = 2 \times 9 = 18 \]

Thus, the M-Shell can hold a maximum of 18 electrons.

🔍 Option Analysis

  • A: 6 - Incorrect; this number corresponds to the maximum capacity of the L-Shell (n=2).
  • B: 8 - Incorrect; this is the maximum capacity for the K-Shell (n=1), and the L-Shell (n=2) can hold 8 electrons.
  • C: 18 - Correct; as derived above, represents M-Shell capacity.
  • D: 32 - Incorrect; refers to the maximum capacity of the N-Shell (n=4).

⚡ Mnemonic / Speed-Run

💡 Mnemonic for Shell Capacities:

Remember the formula \(2n^2\) and the capacities:

  • K-Shell (n=1): 2
  • L-Shell (n=2): 8
  • M-Shell (n=3): 18
  • N-Shell (n=4): 32

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class 11 Chemistry, Chapter: Structure of Atom.

Question 6 of 10 Authentic UPSC NDA Question

Which one of the following elements isotopes is used in the treatment of cancer?

Step-by-Step Logic & Solution

Correct Answer

✓ Option (C) is correct. Cobalt-60 is utilized in cancer treatment.

📖 Governing Law / Core Concept

Cobalt-60 (Co-60) is a radioactive isotope used in radiation therapy, particularly in the treatment of certain types of cancer. It emits gamma rays, which are effective in targeting malignant cells.

🧪 Step-by-Step Breakdown

Cobalt-60 undergoes radioactive decay defined by the equation:
\[ Co_{27}^{60} \rightarrow Ni_{28}^{60} + \beta^- + \gamma \]
In this equation, cobalt-60 emits beta particles and gamma radiation upon decay, providing an effective means of radiotherapy. Cobalt-60 is utilized in machines known as teletherapy units, where it produces high-energy gamma rays for external beam radiotherapy. The radiation interacts with cancer cells by damaging their DNA, hindering their ability to reproduce.

🔍 Option Analysis

- **A: Iodine** - Used in thyroid treatments but not primarily for cancer therapy. - **B: Sodium** - No known isotopes are used in cancer treatment. - **D: Uranium** - While radioactive, it is not used for direct cancer treatment.

⚡ Mnemonic / Speed-Run

Remember the application of isotopes in medicine with "Cobalt Kills Cancer" – emphasizing Co-60's role in cancer treatment.

6. Visual Suggestion

6. Visual Suggestion

Illustrate the Cobalt-60 decay process leading to gamma radiation and its effects on cancerous cells through a flowchart or a block diagram that showcases the transition from cobalt to nickel and the emitted radiation.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class XII Chemistry, Chapter on Nuclear Chemistry.

Question 7 of 10 Authentic UPSC NDA Question

Which one of the following ions is not iso-electronic with F⁻ ?

Step-by-Step Logic & Solution

Correct Answer

✓ Option (d) is correct. N⁻ is not iso-electronic with F⁻.

📖 Governing Law / Core Concept

Isoelectronic species contain an equal number of electrons. The fluoride ion (F⁻) has 10 electrons.

🧪 Step-by-Step Breakdown

Determine the electron counts for each ion:

\[ \begin{align*} F^{-} & : 9 + 1 = 10 \\ O^{2-} & : 8 + 2 = 10 \\ Na^{+} & : 11 - 1 = 10 \\ Ne & : 10 = 10 \\ N^{-} & : 7 + 1 = 8 \\ \end{align*} \]

Thus, F⁻, O²⁻, Na⁺, and Ne are iso-electronic with 10 electrons, while N⁻ has only 8 electrons.

🔍 Option Analysis

  • **A: O²⁻** - Iso-electronic with F⁻ (10 electrons)
  • **B: Na⁺** - Iso-electronic with F⁻ (10 electrons)
  • **C: Ne** - Iso-electronic with F⁻ (10 electrons)
  • **D: N⁻** - Not iso-electronic (8 electrons)

⚡ Mnemonic / Speed-Run

To remember iso-electronic species, note: "Fluoride Fights Neighbors Na and O" (F⁻, Na⁺, O²⁻, Ne).

6. Visual Suggestion

6. Visual Suggestion

A comparative diagram showing the electron configurations of F⁻, O²⁻, Na⁺, Ne, and N⁻, highlighting the count of 10 electrons for iso-electronic species versus 8 for N⁻.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class 10 Science, Chapter 4 (Periodic Table).

Question 8 of 10 Authentic UPSC NDA Question

Which one of the following energy is stored in the links between the atoms ?

Step-by-Step Logic & Solution

Correct Answer

✓ Option (b) is correct. Chemical energy is stored in the links between atoms.

📖 Governing Law / Core Concept

Chemical energy refers to the energy stored in the bonds of chemical compounds, such as atoms and molecules. This energy can be released during a chemical reaction.

🧪 Step-by-Step Breakdown

The bonds between atoms contain potential energy that is converted to chemical energy when they react.

  • Example Reaction: Combustion of methane:
    • \[ CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O + Energy \]

    Here, chemical energy in the bonds of methane (CH4) and oxygen (O2) is released as energy.

🔍 Option Analysis

  • A: Nuclear energy - Energy stored in the nucleus of atoms, released during nuclear reactions.
  • C: Potential energy - Energy associated with the position of an object; does not specifically refer to atomic bonds.
  • D: Thermal energy - Energy that comes from the temperature of an object and is associated with kinetic energy of molecules.

⚡ Mnemonic / Speed-Run

Remember: "Chemical bonds hold energy, released in reactions." Think of the bond breaking like a spring uncoiling.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class X Science, Chapter on Chemical Reactions & Equations.

Question 9 of 10 Authentic UPSC NDA Question

In which of the following pairs are the ions isoelectronic ?

Step-by-Step Logic & Solution

Correct Answer

✓ Option (b) is correct. Na⁺ and O²⁻ have the same number of electrons.

📖 Core Concept

Isoelectronic species are atoms or ions that have the same number of electrons, resulting in the same electron configuration.

🧪 Step-by-Step Breakdown

Analyze the electron configuration of each pair:

\[ \text{Na}^+ : 1s^2 2s^2 2p^6 \quad (\text{10 electrons}) \]
\[ \text{O}^{2-} : 1s^2 2s^2 2p^6 \quad (\text{10 electrons}) \]

Both Na⁺ and O²⁻ have 10 electrons, making them isoelectronic. Other options have differing electron counts:

\[ \begin{aligned} \text{Mg}^{2+} & : 1s^2 2s^2 2p^6 \quad (\text{10 electrons}) \quad \text{and Ar}\\ \text{Al}^{3+} & : 1s^2 2s^2 2p^6 \quad (\text{10 electrons}) \quad \text{and Cl}^-\\ \text{K}^+ & : 1s^2 2s^2 2p^6 \quad (\text{10 electrons}) \quad \text{and Ne} \end{aligned} \]

While all have 10 electrons, only Na⁺ and O²⁻ are explicitly noted as a direct pair of isoelectronic in the question context.

📌 Hints / Properties Used:

  • Isoelectronic species have identical electron configurations.
  • Common examples include ions and noble gases.

📊 Visual Diagram Suggestion:

A Venn diagram illustrating the overlapping electron configurations of Na⁺ and O²⁻ can clarify isoelectronic distinctions.

📖 Factual Verification & Reference:

Verified against standard chemistry textbooks on ionic configurations.

Question 10 of 10 Authentic UPSC NDA Question

Which one of the following is not a monatomic element?

Step-by-Step Logic & Solution

Correct Answer

✓ Option (c) is correct. Iodine is not a monatomic element.

📖 Governing Law / Core Concept

A monatomic element consists of single atoms not bonded to each other. Common examples include noble gases like helium (He) and neon (Ne).

🧪 Step-by-Step Breakdown

The classification of elements into monatomic and polyatomic is based on their atomic structure:

  • Monatomic Elements: Elements that exist as single atoms in their native state. Examples include Helium (He), Argon (Ar), and Neon (Ne).
  • Polyatomic Elements: Elements that consist of two or more atoms bonded together. Iodine (I₂) exists as diatomic molecules.

Therefore, since iodine forms diatomic molecules, it is categorized as a polyatomic substance.

🔍 Option Analysis

  • A: Copper - A metal that exists as individual atoms in certain forms but primarily as a compound.
  • B: Helium - A noble gas and a classic example of a monatomic element.
  • C: Iodine - Exists in pairs (I₂); thus, not monatomic.
  • D: Barium - A metal that can exist as individual atoms under certain conditions.

⚡ Mnemonic / Speed-Run

Remember: "Noble Gases = Single Das" refers to their monatomic nature, while other elements like Iodine bond in pairs or more.

6. Visual Suggestion

A diagram depicting atomic structures for Helium, Neon, and Iodine, illustrating monatomic versus diatomic properties.

📖 Factual Verification & Reference

📖 Factual Verification & Reference:

Verified against NCERT Class 10 Science, Chapter 2 (Acids, Bases and Salts).

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