Chemistry Atomic Structure MDCAT 2017
PMDC Verified Question 80 of 95
Number of electrons in \( ^{71}_{31}\text{Ga}^{+3} \) will be
A
\( 29 \)
B
\( 30 \)
C
\( 34 \)
D
\( 28 \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: \( 28 \)
Concept: A positive ion (cation) is formed when a neutral atom loses electrons. The net positive charge equals the number of electrons lost.

Formula: $$ \text{Electrons} = Z - \text{Charge} $$

Solution:
  • The atomic number of Gallium (Ga) is given as \( Z = 31 \).
  • A neutral atom of Ga has 31 electrons.
  • The \( +3 \) charge indicates the loss of 3 electrons.
  • Total electrons = \( 31 - 3 = 28 \).


Why other options are incorrect: 34 would mean it gained 3 electrons (anion). 29 and 30 miscalculate the subtraction.

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