Chapter Exam

Chapter 7: Classification of Elements – The Periodic Table — Online MCQ Test

Q: Who proposed the Triads classification system for elements?

Answer: A. Johann Dobereiner — Dobereiner observed that certain elements with similar properties occurred in groups of three (triads), where the atomic mass of the middle element was the average of the other two.

Q: Newlands' Law of Octaves stated that properties of elements repeat after every _____ elements.

Answer: C. 8 elements — Newlands observed that when elements were arranged in order of increasing atomic mass, every eighth element had similar properties to the first element, similar to musical octaves.

PHYSICAL SCIENCES · CLASS 10th · Telangana State Board

Practice Chapter 7: Classification of Elements – The Periodic Table with a free chapter-wise online MCQ test for Telangana State Board CLASS 10th PHYSICAL SCIENCES. This chapter covers: This chapter traces the historical evolution of classifying chemical elements from Dobereiner's Triads and Newlands' Law of Octaves to Mendeleev's Periodic Table and the Modern Per.... AI-generated questions from basic to board-exam level, with instant results and explanations.

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Chapter 7: Classification of Elements – The Periodic Table — Important Questions & Answers (FAQ)

Frequently asked questions from Telangana State Board CLASS 10th PHYSICAL SCIENCES — Chapter 7: Classification of Elements – The Periodic Table, with answers and explanations. These are sample questions; the exam has its own separate question set.

Who proposed the Triads classification system for elements?

A. Johann Dobereiner ✓
B. John Newlands
C. Dmitri Mendeleev
D. Henry Moseley

Answer: A. Johann Dobereiner
Dobereiner observed that certain elements with similar properties occurred in groups of three (triads), where the atomic mass of the middle element was the average of the other two.

Newlands' Law of Octaves stated that properties of elements repeat after every _____ elements.

A. 3 elements
B. 7 elements
C. 8 elements ✓
D. 10 elements

Answer: C. 8 elements
Newlands observed that when elements were arranged in order of increasing atomic mass, every eighth element had similar properties to the first element, similar to musical octaves.

Which of the following is NOT a periodic trend observed in the modern periodic table?

A. Atomic radius decreases from left to right in a period
B. Electronegativity increases from left to right in a period
C. Ionization energy increases from top to bottom in a group ✓
D. Metallic character decreases from left to right in a period

Answer: C. Ionization energy increases from top to bottom in a group
Ionization energy actually decreases from top to bottom in a group because atomic radius increases and electrons are farther from the nucleus.

Compare the atomic radius of Sodium (Na) and Chlorine (Cl) in Period 3. Which statement is correct?

A. Na has larger atomic radius because it has fewer valence electrons ✓
B. Cl has larger atomic radius because it is farther from the nucleus
C. Na has larger atomic radius because it has more shells
D. Cl has larger atomic radius because electronegativity increases across the period

Answer: A. Na has larger atomic radius because it has fewer valence electrons
Atomic radius decreases from left to right across a period due to increasing nuclear charge pulling electrons closer; Na (leftmost) has larger radius than Cl.

A student observes that element A (atomic number 12) has lower ionization energy than element B (atomic number 11). This observation contradicts the expected periodic trend. What is the most likely explanation?

A. The student made a measurement error; the data must be incorrect
B. Element A is in a different period than element B, so trends don't apply
C. Element B is in Group 1 with only one valence electron, while element A is in Group 2 with two valence electrons; the single valence electron of B is easier to remove ✓
D. Electronegativity values override ionization energy trends in this case

Answer: C. Element B is in Group 1 with only one valence electron, while element A is in Group 2 with two valence electrons; the single valence electron of B is easier to remove
Na (Z=11) is in Group 1 with a single, loosely-held valence electron, making it easier to ionize than Mg (Z=12) in Group 2 with a more stable two-electron valence shell, despite Na having lower atomic number.

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