What are the characteristics of Democritus’ atom that the author is eager to understand?
I. The atom is quite similar to helium or hydrogen,
II.The atom would be one of tiniest constituents of the universe.
III.The atom would not be further reducible
IV. The atom would not obey any laws.
II and III
The author has clearly ruled out statements (I) in the third sentence of the third paragraph.
The author has mentioned that helium etc. are big and clumsy. Even particles such as proton are buckets full of still smaller objects. So, atom of Democritus must be among the tiniest constituents of the universe. Thus, statements (II) is correct.
The atom cannot be further cut into pieces and hence must be irreducible. This makers assertion (III) correct.
In physical science there cannot be a constituent that does not follow any law. The laws may be arcane and complex through. Moreover, author has not made any such observation. Hence, the statements (IV) are not correct. Hence (b).