Which one of the following elements does not form solid hydrogen carbonate?

Among the alkali metals, lithium is the only element that does not form a solid hydrogen carbonate (bicarbonate). While sodium, potassium, and caesium form stable solid hydrogen carbonates like NaHCO3, KHCO3, and CsHCO3 [2], lithium hydrogen carbonate (LiHCO3) exists only in aqueous solution. This anomaly is attributed to the high polarizing power of the small Li+ ion, which destabilizes the large, polarizable hydrogen carbonate anion in the solid lattice. In contrast, larger alkali metal cations like Na+, K+, and Cs+ can stabilize the solid bicarbonate structure through extensive hydrogen bonding networks [1]. Consequently, when a solution of lithium hydrogen carbonate is evaporated, it decomposes into solid lithium carbonate (Li2CO3), water, and carbon dioxide rather than crystallizing as a solid bicarbonate.

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1. [2] https://www.sciencedirect.com/science/article/abs/pii/S0009261423003603