Question

select all the true statements. the cl⁻ and br⁻ ions have the same number of electrons. the fe²⁺ and fe³⁺ ions have the same number of protons. anions carry a positive charge. the k⁺ ion is formed when a potassium atom loses one electron. the cu⁺ and cu²⁺ ions have the same number of electrons. when an atom gains an electron, it becomes a cation.

Explanation:

1. For "The $\ce{Cl^-}$ and $\ce{Br^-}$ ions have the same number of electrons": Chlorine has an atomic number of 17, so $\ce{Cl^-}$ has $17 + 1 = 18$ electrons. Bromine has an atomic number of 35, so $\ce{Br^-}$ has $35 + 1 = 36$ electrons. They don't have the same number of electrons, so this is false.
2. For "The $\ce{Fe^{2+}}$ and $\ce{Fe^{3+}}$ ions have the same number of protons": Both are iron ions, so they have the same atomic number (26), meaning the same number of protons. This is true.
3. For "Anions carry a positive charge": Anions are formed by gaining electrons, so they carry a negative charge. This is false.
4. For "The $\ce{K^+}$ ion is formed when a potassium atom loses one electron": A potassium atom has 19 electrons. Losing one electron gives it 18 electrons, forming $\ce{K^+}$. This is true.
5. For "The $\ce{Cu^+}$ and $\ce{Cu^{2+}}$ ions have the same number of electrons": $\ce{Cu^+}$ is formed by losing 1 electron, $\ce{Cu^{2+}}$ by losing 2 electrons from a copper atom. So they have different numbers of electrons. This is false.
6. For "When an atom gains an electron, it becomes a cation": Gaining an electron gives a negative charge (anion), losing gives positive (cation). This is false.

Answer:

B. The $\ce{Fe^{2+}}$ and $\ce{Fe^{3+}}$ ions have the same number of protons.
D. The $\ce{K^+}$ ion is formed when a potassium atom loses one electron.