Answer choices are:
A. These elements did not fit in with his pattern.
B. These elements are gases and he didn't include gases.
C. The atoms of these elements had no atomic mass.
D. These elements had not yet been discovered.
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Correct answer choice is:
D. These elements had not yet been discovered.
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Explanation:
Mendeleev would have no precise logic to presume there were lacking elements when they can be distributed by various units. But he did note bearings and was capable to divine some holes based on these bearings. The whole column of noble gases, though, could be dropped as it was a periodic recess, not a recess in the period.
Mendeleev added the noble gases later, near the edge of his life, during enough proof was received.
