In Mendeleev's Periodic Table,the elements were arranged in the increasing order of their atomic masses. However,cobalt with an atomic mass of $58.93 \ amu$ was placed before nickel having an atomic mass of $58.71 \ amu$. Give the reason for the same.

  • A
    Cobalt has higher chemical reactivity.
  • B
    Elements with similar properties were grouped together.
  • C
    Nickel was discovered later.
  • D
    Atomic mass measurements were inaccurate at that time.

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Similar Questions

State Mendeleev's Periodic Law.

Which group of elements could be placed in Mendeleev's Periodic Table without disturbing the original order? Give reason.

$K$ and $Ca$ have atomic numbers $19$ and $20$ respectively,and they belong to the same period.
$(a)$ Which among them would have a smaller atomic size?
$(b)$ Which one would be more electropositive?
$(c)$ To which group would each of them belong?

Which of the following are the characteristics of isotopes of an element?
$(i)$ Isotopes of an element have same atomic masses
$(ii)$ Isotopes of an element have same atomic number
$(iii)$ Isotopes of an element show same physical properties
$(iv)$ Isotopes of an element show same chemical properties

It was assumed by Newlands that only :

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