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JEE Main levelOne or more correct optionsDifficulty 2 of 3pt055

Select the correct statement(s) about the development of the periodic law.

  1. AMendeleev left gaps in his table for elements that were undiscovered at that time.
  2. BThe modern periodic law is based on atomic mass.
  3. CMoseley's X-ray work showed that atomic number is the basis for ordering elements.
  4. DThe position of Ar before K in the modern table is consistent with their atomic numbers.

Answer: A, C, D

Mendeleev left gaps and predicted eka-elements, so A is true. The modern law is based on atomic number, not mass, so B is false. Moseley's work established atomic number, so C is true, and Ar (18) precedes K (19), so D is true.
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