Question

At the time of Newlands, how many elements were known?
A) 50
B) 52
C) 54
D) 56

Answer 1

Hint: Newlands law of octaves, was given by John Alexander Newland, and in 1865, He arranged the 56 elements into octaves. He arranged the elements in increasing order of atomic weights and found that every 8th element shows similar properties with the 1st element.

Complete answer:
John Newlands has seen many similarities in nature. This led him to similarity, of law of octaves of music – ‘Sa’ ‘Re’ ‘Ga’ ‘Ma’ ‘Pa’ ‘Da’ ‘Ni’, then ‘Sa’ again or in English music notes ‘do’ ‘re’ ‘mi’ ‘fa’ ‘so’ ‘la’ ‘ti’ then ‘do’ again.
Newland gave Newlands law of octaves- When elements are arranged in increasing order to atomic masses, then every eighth element has the similar properties to that of the first element.
Newland was among the first one to start classification on the basis of atomic weight.

Thus the correct option is (D) 56.

Additional Information: He could classify only elements upto calcium, out of 56 known elements at his time.
In order to fit in his table, He kept 2 elements in one slot which may differ in property.
Some similar properties elements were separated far apart. Like Iron was kept far apart from Cobalt, Nickel, which has similar property.
The noble gases were not discovered, and thus they were not present in Newlands Table. When noble gases were discovered then, the periodicity in properties was in the 9th element, similar properties were after 8th element.

Note: Till the time of Newland’s classification, the noble gases were not discovered. So we don't see noble gases in Newlands Octaves.
There were multiple drawbacks for Newlands classification, so many people in the scientific community rejected his theory and disagreed with him. But as he was one among few to take atomic mass as reference for classification.