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West Bengal Madhyamik (Class 10) — free MCQ practice

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West Bengal Madhyamik (Class 10) subjects

Chemistry (30)

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ChemistryClass 10 SciencePeriodic Classification of Elements

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Dobereiner grouped elements with similar properties into sets of three called:Read the answer and worked solution →In a Dobereiner triad, the atomic mass of the middle element is roughly the:Read the answer and worked solution →Lithium, sodium and potassium have atomic masses 6.9, 23.0 and 39.0. The average of the first and last is:Read the answer and worked solution →Dobereiner's system failed because he could identify only how many triads?Read the answer and worked solution →

Worked practice questions

Dobereiner grouped elements with similar properties into sets of three called:

  1. Triads
  2. Trends
  3. Tracks
  4. Traces
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Correct answer: A. Triads

1. He searched for families of similar elements. 2. Each family he found held three members. 3. He called them triads. _Source: syllabus Science Class X, Chapter 5, Periodic Classification of Elements._

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In a Dobereiner triad, the atomic mass of the middle element is roughly the:

  1. Average of volumes
  2. Average of others
  3. Average of shells
  4. Average of charges
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Correct answer: B. Average of others

1. The three are written in order of rising atomic mass. 2. The middle one sits halfway between the outer two. 3. So it is the average of the others. _Source: syllabus Science Class X, Chapter 5, Periodic Classification of Elements._

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Lithium, sodium and potassium have atomic masses 6.9, 23.0 and 39.0. The average of the first and last is:

  1. 22.95
  2. 20.95
  3. 24.95
  4. 26.95
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Correct answer: A. 22.95

1. Add 6.9 and 39.0 to get 45.9. 2. Half of 45.9 is 22.95. 3. So the average is 22.95. _Source: syllabus Science Class X, Chapter 5, Periodic Classification of Elements._

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