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

$Li, Be, B$ and $C$ are the elements of the same period of the Modern Periodic Table.
$(a)$ Arrange them in increasing order of their atomic size.
$(b)$ In which shell (number) would the last electron enter for all of them?
$(c)$ Calculate the number of valence electrons in each.
$(d)$ Which element amongst them is most electropositive?

Write the formula of the product formed when the element $A$ (atomic number $19$) combines with the element $B$ (atomic number $17$). Draw its electronic dot structure. What is the nature of the bond formed?

Write true or false for the statement: Metallic character decreases across a period and increases down a group because the effective nuclear charge acting on the valence shell electrons increases across a period and decreases down the group.

Where would you locate the element with electronic configuration $2, 8$ in the Modern Periodic Table?

Arrange the following elements in increasing order of their atomic radii.
$(a)$ $Li, Be, F, N$
$(b)$ $Cl, At, Br, I$

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