Which of the following is a Lewis acid ?

Correct answer: 1) 

Concept:

• Lewis acids are the acids that can accept the paired electrons or they are having some vacant orbitals to fill the electrons.
• Arrhenius acids: According to Arrhenius, the Arrhenius acids are the acids that give ions when the acids are dissolved in the water.
• Bronsted Lowry acids: According to Bronsted, the Bronsted Lowry acids are the acids that are proton donors, i.e., acids that have the tendency to donate protons.

Explanation:

• Alkaline earth metals form ionic chloride whereas aluminum chloride is covalent.
• Despite sharing electrons with chlorine, the octet of aluminum is incomplete.
• To complete the octet, it needs electrons and thus, acts as a Lewis acid.
• AlCl₃ is an example of Lewis acid.
• So, from analyzing the definition of the Lewis acid, we will see all the options.
• In the first option,  AlCl₃ has vacant orbitals. So, AlCl₃ is a Lewis acid.
• In the second option,  MgCl₂ has no vacant orbitals. So,  MgCl₂ is not a Lewis acid.
• In the third option,  CaCl₂ has no vacant orbitals. So,  CaCl₂ is not a Lewis acid.
• In the last option,  BaCl₂ has no vacant orbitals. So,  BaCl₂ is not a Lewis acid.

Conclusion:

Hence,  AlCl₃ is an example of Lewis acid.

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