iGCSE Chemistry (0620) Core:2.4 Ions and ionic bonds: Exam Style Questions Paper 1- New Syllabus
▶️ Answer/Explanation
Detailed solution:
Potassium iodide (KI) is an ionic compound. Statement 1 is incorrect: potassium forms positive ions (cations, K⁺), while iodide forms negative ions (anions, I⁻). Statement 2 is correct: like other ionic compounds, potassium iodide conducts electricity when molten or dissolved in water because the ions become free to move. Statement 3 is incorrect: potassium and iodine form an ionic bond by transferring electrons, not sharing them. Therefore, only statement 2 is correct.
▶️ Answer/Explanation
Detailed solution:
Rubidium (Rb) is in Group I, so it has one electron in its outer shell. To achieve a stable noble gas configuration, it loses that one electron easily. Losing an electron forms a positive ion with a 1+ charge, written as $\text{Rb}^+$. So, the electron change is “electron lost” and the formula is $\text{Rb}^+$, as shown in row C.
▶️ Answer/Explanation
Detailed solution:
In the reaction between sodium and chlorine, sodium atoms from Group I want to lose one electron to get a full outer shell, and chlorine atoms from Group VII want to gain one electron to achieve the same stable configuration. So each chlorine atom gains one electron to become a $Cl^{-}$ ion. Gaining or losing a proton is not possible in a chemical reaction because that would change the element’s identity, so the word “proton” acts as a distractor here.