An entire group of elements was unknown when the periodic table was first developed because they were unreactive and no known compounds were composed of them. What most likely led to the inclusion of these elements in the periodic table?
the formation of a compound in the laboratory
new technology that showed how to identify one of the elements
improvements in instruments to measure small masses
more careful experiments to create synthetic elements

The correct option is;

New technology showed how to identify one of the elements

Explanation:

The unexpected discovery of argon, which is one of the inert gases, by Lord Rayleigh in 1892, when he observed while attempting to determine more reliable atomic weights by carrying out gas density measurements through experiments that yielded more exact results, that the density of nitrogen obtained from the atmosphere was different from that from pure ammonia

The suspected gas which was the cause of the observation was isolated by removing all the other known gases in the air and with the aid of its emission spectra, which was a new technique of distinguishing materials, metals and gases, William Ramsay was able to show that it was a new chemical species.

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explanation:

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if you're asking what comes out, it's steam.