\textbf{84 --} Which of the following is correct?
\textbf{A: In stable ions of main-group metals, the number of electrons in all sub-shells is even.}
\textbf{B: Stable ions formed from atoms $_{31}\text{Ga}$ and $_{30}\text{Zn}$ have similar electron configurations.}
\textbf{C: The color of vanadium salt solution changes from yellow to purple upon reaction with iron metal dust.}
\textbf{D: The use of plants that absorb metals is one of the appropriate methods for extracting nickel, copper, and gold.}
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(1) ``A'' and ``C'' \hspace{1cm} (2) ``A'' and ``B'' \hspace{1cm} (3) ``B'' and ``D'' \hspace{1cm} (4) ``B'' and ``D''
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