Alkali metals are not found in free state due to their highly reactive nature. This is due to

Options

A. their large size and low ionisation enthalpy
B. their large size and high ionisation enthalpy
C. their low ionisation enthalyp and high electron gain enthalpy
D. their tendency to impart colour to the flame.

Answer

### Step-by-Step Solution:

1. **Understanding Alkali Metals**: Alkali metals belong to Group 1 of the periodic table and include elements like lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). They are characterized by having a single electron in their outermost shell.

2. **Electronic Configuration**: The electronic configuration of alkali metals is represented as \( ns^1 \), where \( n \) is the principal quantum number corresponding to the outermost shell. This means that they have one electron in their outermost shell.

3. **Tendency to Lose Electrons**: Alkali metals tend to lose this single outer electron easily to achieve a stable noble gas configuration. This process is driven by the desire to attain a full outer shell, which is energetically favorable.

4. **Reactivity and Ionization Energy**: The reactivity of alkali metals is primarily due to their low ionization enthalpy, which is the energy required to remove an electron from an atom. Since alkali metals have a low ionization enthalpy, they can lose their outer electron readily, making them highly reactive.

5. **Atomic Size and Reactivity**: As we move down the group in the periodic table, the atomic size of alkali metals increases due to the addition of electron shells. This increase in size results in a weaker attraction between the nucleus and the outermost electron, making it even easier to lose that electron.

6. **Conclusion**: Due to their large atomic size and low ionization enthalpy, alkali metals are highly reactive and are not found in their free state in nature. Instead, they are typically found in compounds such as metal oxides or metal carbonates.

### Final Answer:
Alkali metals are not found in free state due to their highly reactive nature, which is attributed to their large size and low ionization enthalpy.

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