Question

he, ne, and ar have similar chemical and physical properties. the mass of ne is very close to the average mass of he and ar. which periodic pattern would this fit?
the law of octaves (newlands)
the octet rule (lewis)
periodic law (moseley)
law of triads (dobereiner)

Explanation:

Dobereiner's Law of Triads states that when elements are arranged in groups of three (triads) with similar chemical and physical properties, the atomic mass of the middle - element is approximately the average of the atomic masses of the other two. He, Ne, and Ar with Ne having a mass close to the average of He and Ar's masses fit this pattern. The Law of Octaves is about elements repeating properties every eighth element, the Octet Rule is about the stability of atoms having eight valence electrons, and Moseley's Periodic Law is based on atomic number.

Answer:

D. Law of Triads (Dobereiner)