Which of the following ions will form a compound with the bicarbonate ion (HCO_3^-) in a 1:1 cation to anion ratio?

• A. Mg^{2+}
• B. Ca^{2+}
• C. Na^+
• D. Al^{3+}

Answer: (C)

Verified step by step guidance

1. Identify the charge on the bicarbonate ion, which is \(\mathrm{HCO_3^-}\), meaning it has a charge of \(-1\).
2. Understand that to form a compound with a 1:1 cation to anion ratio, the positive charge of the cation must balance the negative charge of the bicarbonate ion exactly.
3. Check the charges of the given cations: \(\mathrm{Mg^{2+}}\) has a charge of \(+2\), \(\mathrm{Ca^{2+}}\) has a charge of \(+2\), \(\mathrm{Na^+}\) has a charge of \(+1\), and \(\mathrm{Al^{3+}}\) has a charge of \(+3\).
4. Since the bicarbonate ion has a charge of \(-1\), only a cation with a \(+1\) charge will combine in a 1:1 ratio to balance the charges without needing multiple ions.
5. Therefore, the ion that will form a compound with bicarbonate in a 1:1 ratio is the sodium ion, \(\mathrm{Na^+}\).