Which alkali metal during flame test will show colour corresponding to maximum wavelength?

Options

A. Li
B. Na
C. K
D. Cs

Explanation

To solve the question of which alkali metal shows a color corresponding to the maximum wavelength during a flame test, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Flame Tests**: Alkali metals, when heated, impart characteristic colors to flames due to the excitation of their outermost electron. When these excited electrons return to their ground state, they emit energy in the form of light.

2. **Identifying Alkali Metals**: The alkali metals include Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), and Cesium (Cs). Each of these metals emits a different color when subjected to a flame test.

3. **Color and Wavelength Relationship**: The color emitted by an element in a flame test is related to the wavelength of the light. Generally, longer wavelengths correspond to colors like red, while shorter wavelengths correspond to colors like blue or violet.

4. **Ionization Energy Consideration**: Alkali metals have varying ionization energies. Lithium has the highest ionization energy among the alkali metals, which means it requires more energy to excite its electron. As a result, it emits light at a longer wavelength (red).

5. **Comparison of Emitted Colors**:
- Lithium emits a crimson red color.
- Sodium emits a bright yellow color.
- Potassium emits a lilac color.
- Rubidium emits a red-violet color.
- Cesium emits a blue color.

6. **Conclusion**: Since red light has the longest wavelength in the visible spectrum, and Lithium emits a crimson red color, we can conclude that Lithium corresponds to the maximum wavelength among the alkali metals during a flame test.

### Final Answer:
The alkali metal that will show color corresponding to maximum wavelength during a flame test is **Lithium (Li)**, which imparts a crimson red color to the flame.

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