Q18 / 200 · Manipal (MET) 2014 · Chemistry

Which of the following sets of quantum numbers could represent the last electron added to complete the electron configuration for a ground state atom of $\operatorname{Br}(Z=35)$ according to the Aufbau principle, $n ; l ; m_l ; m_s$

  • A
    $4 ; 0 ; 0 ;-\frac{1}{2}$
  • Correct answer
    B
    $4 ; 1 ; 1 ;-\frac{1}{2}$
  • C
    $3 ; 1 ; 1 ;-\frac{1}{2}$
  • D
    $4 ; 1 ; 2 ;+\frac{1}{2}$

Solution

The valence shell configuration is $4 s^2 4 p^5$ and for the last electron $n=4, l=1$ $m=-1,0 \text { or }+1, s=+\frac{1}{2} \text { or }-\frac{1}{2}$
Hence, $4,1,1,-\frac{1}{2}$

Hence, the correct answer is option: 'B'.

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