Which of the following elements was the last element in Newland's Law of Octaves?

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RRB ALP CBT I 31 Aug 2018 Shift 1 Official Paper
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  1. Rubidium
  2. Thorium
  3. Bromine
  4. Hydrogen

Answer (Detailed Solution Below)

Option 2 : Thorium
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Detailed Solution

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The correct answer is Thorium.

Key Points

  • Newland's law of octave states that when elements are arranged in the increasing order of their atomic masses in the periodic table, the properties of the eighth element are a repetition of the first element.
  • John Newlands, an English scientist first arranged this starting with Hydrogen and ending with Thorium (atomic number = 56). Hence option 2 is correct.
  • This law was discovered when none of the inert gases was known.
    • So if we take the elements from Lithium (Li, Z =3) and Sodium (Na, Z = 11), Sodium possesses similar properties to Lithium.

Additional Information

  • Though this law does not apply to the whole table, it is till Calcium only and after that eighth element did not have the properties of the first element.
  • When arranged in the increasing order of their atomic weights, Newland's law of octaves worked mostly with lighter elements.
  • Thorium (Z = 90) is a radioactive metal and is used for ceramics, telescopic and camera lenses, heat-resistant paints, sources of nuclear power etc.
    • It is also used in radiometric dating and strengthening magnesium.
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