Which of the following elements can form a tripositive (3⁺) ion?

Elements in Group 13 of the periodic table, such as aluminium (Al), have three valence electrons in their outermost shell. Aluminium tends to lose all three electrons to achieve a stable noble gas configuration, forming the Al³⁺ ion in ionic compounds like Al₂O₃ and AlCl₃. This is a characteristic property of aluminium and other Group 13 elements.

In contrast, the other elements in the options behave differently:

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  Beryllium (Be) is in Group 2 and usually forms Be²⁺ ions by losing two valence electrons. It does not have enough electrons to form a 3⁺ ion.

  
  


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  Carbon (C) is a non-metal and rarely forms positive ions. It typically forms covalent compounds and does not form a stable C³⁺ ion.

  
  


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  Silicon (Si) is also a metalloid; it forms covalent compounds rather than positive ions and does not produce a 3⁺ ion under normal conditions.

  
  

The ability to form a tripositive ion depends on the element’s position in the periodic table and the number of valence electrons available for loss. Aluminium’s electron configuration is [Ne] 3s² 3p¹, which makes it energetically favorable to lose three electrons and form Al³⁺.

Aluminium ions are widely used in industrial and chemical applications, including alumina production, water purification, and as a component in alloys. Understanding which elements can form specific ions is critical in inorganic chemistry, particularly in predicting compound formation and reactivity.

Thus, among the given elements, the correct answer is Aluminium (D), as it is the only one capable of forming a stable 3⁺ ion.