MPSC Rajyaseva 2019 Prelims General Studies Official Paper I

Concept:A Lewis acid is a species that can accept a lone pair of electrons, usually due to a vacant orbital or electron deficiency.Explanation:Check each option:$\mathrm{BCl}_3$ has an incomplete octet on boron, so it accepts electron pairs.$\mathrm{BF}_3$ also has an incomplete octet on boron and acts as a Lewis acid.$\mathrm{BeCl}_2$ has beryllium with only four valence electrons in the monomer, so it can accept electron pairs.$\mathrm{BaCl}_2$ is ionic and contains $\mathrm{Ba}^{2+}$ and $\mathrm{Cl}^-$ ions.The $\mathrm{Ba}^{2+}$ ion has a stable noble gas configuration $[\mathrm{Xe}]$ and no vacant orbital to accept a lone pair.Therefore, $\mathrm{BaCl}_2$ is not a Lewis acid.Answer:A. Barium chloride ($\mathrm{BaCl}_2$).