Question

Which of the following statement(s) is(are) not correct about Lithium?

• A. Lithium is least reactive of all alkali metals.
• B. It is the weakest reducing agent among all alkali metals.
• C. It forms no acetylides with acetylene.
• D. $LiHC{O}_3$ is a white crystalline solid.

Answer 1

Answer: (B), (C), (D)

The correct options are
B It forms no acetylides with acetylene.
C It is the weakest reducing agent among all alkali metals.
D $LiHC{O}_3$ is a white crystalline solid.

Among alkali metals, lithium has the highest value of ionization energy. But it has a large heat of hydration due to small size. Thus, the hydration energy more than compensates the ionization energy. Hence it is strongest reducing agent among the alkali metals. Hence statement B is incorrect.

The reduction potential values are determined considering various factors like ionization energy and hydration enthalpy. It is the highly negative hydration enthalpy of Lithium cation that makes the cation highly stable in an aqueous medium. But in an organic medium, the hydration does not take place hence the reduction tendency is governed by the ionization energy alone. Since Lithium has a high value of ionization energy, hence it doesn't form a compound with acetylene. Hence statement C is incorrect.

Among the alkali metals, lithium is least electropositive. Li differs from the rest of the family members and shows anomalous behaviour due to the diagonal relationship with $Mg$. Lithium bicarbonate ($LiHC{O}_3$) found in solution form and not known to exist in normal temperature and pressure, while others bicarbonates of alkali metals exist in solid-state. Hence statement D is incorrect.

Hence, the answers are $B,CandD$.