Question

in the formation of an ionic compound, what is the role of the metal atom?
it shares electrons to achieve a stable octet.
it gains electrons to form a negative ion (anion).
it transfers electrons away to form a positive ion (cation).
it acts as a spectator ion, not participating in the transfer.

which ion could a technician add to water to test for chloride ions, cl−?
a. na⁺
b. ag⁺
c. nh₄⁺
d. cu²⁺

Explanation:

First Question (Ionic Compound Formation - Metal Atom Role)

In ionic bonding, metal atoms typically have low electronegativity and few valence electrons. To achieve a stable octet (or duet for some metals like Li, Be), they lose (transfer away) electrons. Losing electrons makes them positively charged ions (cations). Sharing electrons is covalent bonding, gaining electrons is typical of non - metals to form anions, and spectator ions are not involved in the electron transfer during ionic compound formation.

Second Question (Testing for Chloride Ions)

To test for chloride ions ($\ce{Cl-}$), we use the reaction $\ce{Ag+ + Cl-
ightarrow AgCl(s)}$. Silver chloride ($\ce{AgCl}$) is a white, insoluble precipitate. $\ce{Na+}$ will form soluble $\ce{NaCl}$, $\ce{NH4+}$ will form soluble $\ce{NH4Cl}$, and $\ce{Cu^{2+}}$ will not form a precipitate with $\ce{Cl-}$ under typical testing conditions. So $\ce{Ag+}$ is used to test for $\ce{Cl-}$.

Answer:

It transfers electrons away to form a positive ion (cation).