<u>Answer: </u>He sorted on the basis of average atomic weights.
<u>Explanation:</u>
Dmitri Mendeleev in 1863 arranged chemical elements in the groups according to their average atomic weights.
He said that elements which have similar chemical properties either have similar atomic weights or their atomic weights increases regularly.
Hence, he collaborated a great work in sorting the elements according to their average atomic weights.
The best option is <span>D. The orientation of the reactants is critical.
</span><span>Since chlorine and hydrogen both participate in the reaction and speed is not essential.</span>