Animated Solution for Chemistry - s and p-Block Elements: The incorrect statement is

Lithium, the lightest of all solid elements, is the rebel of the alkali metal family. Because of its exceptionally small size and high charge density, it behaves quite differently from its heavier siblings like sodium and potassium. This question is a classic test of how well you understand these anomalous properties.

Let's look at the first claim: Lithium is the strongest reducing agent among the alkali metals.

At first glance, this might seem counterintuitive. Doesn't lithium have the highest ionization energy in its group? Yes, it does. It is the hardest to strip an electron from a gaseous lithium atom. However, reducing power in an aqueous solution is measured by the standard reduction potential ($E^{\circ }$), which is a combination of three energy terms: sublimation energy, ionization energy, and hydration energy.

Because the ${\text{Li}}^{+}$ ion is so tiny, it attracts water molecules fiercely. The energy released during this hydration process is massive—so massive that it more than compensates for the high ionization energy. This makes lithium the strongest reducing agent in the entire electrochemical series!

Next, we consider its reactivity with water. We've all seen videos of sodium or potassium exploding violently when dropped in water. But lithium? It just fizzes and dances around gently.

Why is lithium the least reactive with water? Reactivity is a kinetic phenomenon. Lithium has a higher melting point and a stronger metallic bond. When it reacts with water, the heat generated isn't enough to melt the metal quickly, keeping the surface area small and the reaction rate slow. So, while it is thermodynamically a strong reducing agent, kinetically, it is a slow reactor.

Now we arrive at the core of the problem: the thermal decomposition of nitrates.

When you heat a typical alkali metal nitrate, like sodium nitrate (${\text{NaNO}}_3$), it partially decomposes to form a nitrite and oxygen gas:

But lithium is different. The tiny ${\text{Li}}^{+}$ ion has an incredibly high polarizing power. It pulls strongly on the electron cloud of the large nitrate (${\text{NO}}_3^{-}$) ion, weakening the $\text{N-O}$ bonds. As a result, the nitrate ion completely shatters upon heating, releasing nitrogen dioxide and leaving behind lithium oxide:

Therefore, the statement claiming that ${\text{LiNO}}_3$ gives ${\text{LiNO}}_2$ is incorrect.

Finally, because of that same high charge density, ${\text{Li}}^{+}$ ions are heavily hydrated in aqueous solutions. When you evaporate a solution of lithium chloride, the lithium ions refuse to let go of their water molecules. Thus, it crystallizes as a dihydrate: $\text{LiCl}\cdot 2{\text{H}}_2\text{O}$. Other alkali metal chlorides, like $\text{NaCl}$ or $\text{KCl}$, crystallize as anhydrous salts because their larger cations don't hold onto water as tightly.

Understanding these fundamental differences is key to mastering s-block chemistry!