Which alkali metal emits longest wavelength light in flame test ?

Options

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

Explanation

To determine which alkali metal emits the longest wavelength light in a flame test, we can follow these steps:

### Step 1: Understand the Flame Test
The flame test is a qualitative analysis technique used to identify the presence of certain metal ions based on the characteristic colors they emit when heated in a flame. The color observed is related to the energy transitions of electrons in the metal ions.

### Step 2: Ionization Energy and Wavelength Relation
The energy of the emitted light is inversely related to its wavelength. This means that metals with lower ionization energies tend to emit light at longer wavelengths. Alkali metals have low ionization energies due to their larger atomic sizes as we move down the group.

### Step 3: Identify Alkali Metals
The alkali metals in the periodic table include:
- Lithium (Li)
- Sodium (Na)
- Potassium (K)
- Rubidium (Rb)
- Cesium (Cs)

### Step 4: Compare Ionization Energies
Among the alkali metals, rubidium (Rb) has the lowest ionization energy, followed by potassium (K). This means rubidium would emit the longest wavelength light, but since it is not an option, we look at the next one.

### Step 5: Conclusion
Since rubidium is not provided in the options, potassium (K) will be the alkali metal that emits the longest wavelength light in the flame test among the available choices.

### Final Answer
The alkali metal that emits the longest wavelength light in the flame test is **Potassium (K)**.

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