Atomic vs. Ionic Identity in Iodine

Steps:

• Iodine atom (I) is neutral with 53 protons and 53 electrons; iodide ion (I⁻) has 53 protons and 54 electrons.
• Both share the same atomic number (53), defining them as iodine.
• Isotopes differ in neutrons, not electrons; ions differ in electrons, not protons.
• Evaluate options: only proton count remains identical.

Why C is correct:

• The number of protons (atomic number) identifies the element; all iodine species, including atoms and ions, have 53 protons by definition.

Why the others are wrong:

• A: Isotopes have the same protons but different neutrons; atoms and ions differ in electrons, not neutrons.
• B: Iodide ions react differently due to their negative charge, forming ionic compounds unlike neutral atoms.
• D: Iodide ions are larger and more soluble than atoms, altering physical properties like size and state.

Final answer: C