Given below are two statements:
Statement I: $\mathrm{K>Mg>Al>B}$ is the correct order in terms of metallic character.
Statement II: Atomic radius is always greater than the ionic radius for any element.
In the light of the above statements, choose the correct answer from the options given below:
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Cations shrink, anions expand — always check the charge before comparing radii.
Statement I: K > Mg > Al > B is the correct order in terms of metallic character.
To understand this statement, we need to know the concept of metallic character. It refers to the tendency of an element to lose electrons and form cations.
Metallic character generally decreases across a period from left to right and increases down a group in the periodic table.
Potassium (K), Magnesium (Mg), Aluminium (Al), and Boron (B) are elements in the 3rd period of the periodic table.
Moving from left to right across this period, elements become less metallic.
Therefore, the order of metallic character is K > Mg > Al > B. This makes Statement I true.
Statement II: Atomic radius is always greater than the ionic radius for any element.
A closer examination of this statement shows:
An atomic radius is the measure of the size of an element's atoms, usually the mean or typical distance from the center of the nucleus to the boundary of the surrounding shells of electrons.
An ionic radius is the radius of an atom's ion. Cations (positively charged ions) are smaller than the original atom because they lose electrons, which reduces electron-electron repulsion and allows the electrons to be pulled closer to the nucleus. Anions (negatively charged ions), however, gain electrons and have a larger ionic radius compared to the atomic radius due to increased electron-electron repulsion and added electron shells.
Hence, the statement that the atomic radius is always greater than the ionic radius is false because it does not hold true for anions.
Based on the analysis above, the correct option is: Statement I is true but Statement II is false.
