The INCORRECT statement is

Options

A. Lithium is least reactive with water among the alkali metals
B. LiCl crystallises from aqueous solution as `LiCl.2H_2O`
C. Lithium is the strongest reducing agent among the alkali metals
D. `LiNO_3` decomposes on heating to give `LiNO_2 and O_2`.

Explanation

To determine the incorrect statement regarding lithium among the alkali metals, we will analyze each of the four statements one by one.

### Step 1: Analyze the First Statement
**Statement:** Lithium is least reactive with water among the alkali metals.

**Analysis:** This statement is true. Lithium has a higher activation energy compared to other alkali metals, making it less reactive with water. While it can react with water to form lithium hydroxide (LiOH) and hydrogen gas, it does so less vigorously than sodium or potassium.

**Conclusion:** This statement is correct.

### Step 2: Analyze the Second Statement
**Statement:** LiCl crystallizes from aqueous solution as LiCl·2H2O.

**Analysis:** This statement is also true. Lithium chloride (LiCl) is soluble in water, and when it crystallizes, it forms a hydrated form, specifically LiCl·2H2O, which indicates that two water molecules are associated with each lithium chloride unit.

**Conclusion:** This statement is correct.

### Step 3: Analyze the Third Statement
**Statement:** Lithium is the strong reducing agent among the alkali metals.

**Analysis:** This statement is true as well. Lithium has one electron in its outermost shell, which it can easily lose to achieve a stable electron configuration. This ability to lose an electron makes lithium a strong reducing agent compared to other alkali metals.

**Conclusion:** This statement is correct.

### Step 4: Analyze the Fourth Statement
**Statement:** LiNO3 decomposes on heating to give LiNO2 and O2.

**Analysis:** This statement is incorrect. The decomposition of lithium nitrate (LiNO3) does not yield lithium nitrite (LiNO2) and oxygen (O2). Instead, it decomposes to form lithium oxide (Li2O), nitrogen dioxide (NO2), and oxygen (O2) as per the reaction:
\[ 4 \text{LiNO}_3 \rightarrow 2 \text{Li}_2\text{O} + 4 \text{NO}_2 + \text{O}_2 \]

**Conclusion:** This statement is incorrect.

### Final Conclusion
The incorrect statement is the fourth one: "LiNO3 decomposes on heating to give LiNO2 and O2."

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