Which one of the following is most ionic?
Correct answer: C. KCl
- A. NaCl
- B. MgCl2
- C. KCl
- D. AlCl3
Explanation
The correct answer is KCl because it forms the most ionic bond among the options provided. Potassium (K) is larger and has a lower charge density than sodium (Na), making it easier to lose its valence electron and form a K+ cation. According to Fajan's rules, larger cations with a lower charge density form more ionic bonds, which is why KCl is more ionic than NaCl. NaCl is ionic, but sodium's smaller size compared to potassium leads to a slightly higher charge density, resulting in less ionic character compared to KCl.MgCl2 has a +2 charge on magnesium, which increases the covalent character of the bond due to polarization effects.AlCl3 is more covalent due to aluminum's +3 charge, which causes significant polarization of the chloride ions. The ability of AlCl3 to form a dimer also supports its covalent nature.
This question appeared on the ETEA MDCAT 2014 paper, which you can sit online with every answer explained.
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Periodic properties arise from electron configuration and effective nuclear charge, producing trends in atomic and ionic radius, ionization energy, electron affinity, electronegativity, metallic character and reactivity. Comparisons run across periods and down groups, with attention to common exceptions. The topic also relates these trends to the behavior of s-block and p-block elements.
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