MCQ
The elements $, A, B, C, D$ and $E$ have atomic number $9, 11, 17, 12$ and $13$ respectively. Which pair of elements belong to the same group?
  • A
    $A$ and $B$
  • B
    $B$ and $D$
  • $A$ and $C$
  • D
    $D$ and $E$

Answer

Correct option: C.
$A$ and $C$
Elements having the same number of valence electrons belong to the same group.
Element
Electronic configuration
$A(9)$ $2, 7$
$B(11)$ $2, 8, 1$
$C(17)$ $2, 8, 7$
$D(12)$ $2, 8, 2$
$E(13)$ $2, 8, 3$
As, both $A$ and $C$ elements have the same number of valence electrons which is $7,$ hence they belong to the same group, i.e. $17^{\text {th }}$ group of periodic table.

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