Question

# Statement I : Moseley's plot of square root of frequency vs the position number of elements in periodic table inspired the periodicity to be defined in terms of atomic number instead of atomic weight. Statement II : According to Moseley's law , the frequency of Kα Characteristic x-ray increased with atomic number instead of atomic weight, and he concluded that atomic number is the fundamental quantity which increases in regular steps as one moves from one element to other.

A
Both the statements are correct and Statement II infers Statement I.
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B
Both the statements are correct but Statement II doesn't infer Statement I.
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C
Statement I is correct but II is not.
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D
Statement I is wrong but II is correct.
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Solution

## The correct option is A Both the statements are correct and Statement II infers Statement I.Earlier scientists made the periodic table based on the element’s chemical properties. They observed the increasing order of masses to be the common trend, except at few places. For example: The placement of Nickel and Cobalt in periodic table. The atomic weight of Cobalt was more than Nickel and according to the atomic mass trend should have been placed after Nickel but were placed correctly due to Moseley’s objective measurements of their atomic numbers. Co 27 and Ni 28. Moseley plotted the square root of frequency of Kα Characteristic x-ray of different elements against their position number in the periodic table. He found out the curve to be linear. Moseley found that the frequency of Kα Characteristic x-ray of Nickel was more than that of the Cobalt and thus put Nickel after Cobalt in the periodic table. Moseley was convinced after his characteristic x-ray experiment that, there is another fundamental quantity which increases as regular steps as one moves from one element to the other and that was number of protons (positively charged particles inside the nucleus). Which we know today as Atomic number. Following our discussion, not only both the statements are correct but Statement II infers to Statement I as well.

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