Law of Octaves became irrelevant after the discovery of:

Correct option is D

Correct Answer:(d)Noble gases

• Proposed by John Newlands in 1864, the Law of Octaves stated that elements, when arranged by increasing atomic mass, repeated similar properties every eighth element.
• It was one of the first attempts to classify elements but was limited to lighter elements.
• Discovery of Noble Gases:
• The discovery of noble gases(e.g., helium, neon, argon) introduced a new group of elements with distinct chemical inertness.
• Noble gases did not fit into the octaves pattern and disrupted the periodic recurrence of properties, making the law obsolete.
  

• Isotopes have the same chemical properties but differ in atomic mass. Their discovery highlighted limitations of atomic mass-based classification but did not directly affect the Law of Octaves.

• Fullerene is an allotrope of carbon and does not influence elemental classification.

• The discovery of radioactive elements revealed instability in some nuclei but did not invalidate the concept of periodic properties.