Increasing order of density is

Options

A. `Li lt K lt Na lt Rb lt Cs`
B. `Li lt Na lt K lt Rb lt Cs`
C. `Li lt Na lt K lt Cs lt Rb`
D. `K lt Li lt Na lt RB lt Cs`

Answer

To determine the increasing order of density for the alkali metals, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Density**:
Density is defined as mass per unit volume. In the context of elements, we can express density (D) as:
\[ D = \frac{\text{Atomic Mass}}{\text{Atomic Volume}} \]
Since atomic volume is related to atomic size, we can also say:
\[ D = \frac{\text{Atomic Mass}}{\text{Size}} \]

2. **Analyzing Alkali Metals**:
The alkali metals (Group 1 elements) include Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), and Cesium (Cs). As we move down the group, both atomic mass and atomic size increase.

3. **Trends in Atomic Mass and Size**:
- **Atomic Mass**: Increases down the group (Li < Na < K < Rb < Cs).
- **Atomic Size**: Also increases down the group (Li < Na < K < Rb < Cs).

4. **Comparing Mass and Size**:
Although both mass and size increase down the group, the increase in atomic mass is more significant than the increase in atomic size. This means that the density will generally increase down the group.

5. **Special Case of Potassium**:
However, it is important to note that between Sodium (Na) and Potassium (K), Potassium has a larger atomic size which leads to a lower density compared to Sodium. Therefore, even though Potassium has a higher atomic mass, its density is lower than that of Sodium.

6. **Establishing the Order**:
Considering the above points, the increasing order of density for the alkali metals is:
\[ \text{Li} < \text{K} < \text{Na} < \text{Rb} < \text{Cs} \]

### Final Answer:
The increasing order of density is:
\[ \text{Li} < \text{K} < \text{Na} < \text{Rb} < \text{Cs} \]