Iodine atoms and ions differ by electrons but share protons

Steps:

• Identify iodine atom as neutral with 53 protons, 53 electrons, and typically 74 neutrons.
• Recognize iodide ion (I⁻) as iodine atom gaining one electron, resulting in 53 protons and 54 electrons.
• Confirm both have atomic number 53, meaning identical proton count.
• Distinguish that ionization changes charge and electron count but not protons or neutrons.

Why C is correct:

• Atomic number defines the element; iodine's atomic number 53 means all its atoms and ions have exactly 53 protons.

Why the others are wrong:

• A: Isotopes have the same protons but different neutrons; atom and ion differ in electrons, not neutrons.
• B: Iodide ions, being charged, form different compounds (e.g., salts) than neutral atoms.
• D: Ions have distinct physical properties like higher solubility in water due to charge.

Final answer: C