Which one of the following is most reactive? Li Na K Rb

Options

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

Explanation

To determine which of the given elements (Li, Na, K, Rb) is the most reactive, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Group**:
All four elements (Li, Na, K, Rb) belong to Group 1 of the periodic table, which is known as the alkali metals.

**Hint**: Remember that elements in the same group have similar properties, including reactivity.

2. **Understand Reactivity in Alkali Metals**:
The reactivity of alkali metals increases as you move down the group. This is due to the increase in atomic size and the decrease in ionization energy.

**Hint**: Think about how atomic size and ionization energy affect the ability of an element to lose its outermost electron.

3. **Compare Atomic Sizes**:
- Lithium (Li) has the smallest atomic size.
- Sodium (Na) is larger than Lithium.
- Potassium (K) is larger than Sodium.
- Rubidium (Rb) is the largest among them.

**Hint**: Larger atomic size means that the outermost electron is further from the nucleus, making it easier to lose.

4. **Evaluate Electropositivity**:
Electropositivity increases down the group. Therefore, Rubidium (Rb), being the largest, will have the highest electropositivity.

**Hint**: Recall that electropositivity is a measure of how easily an atom can lose an electron.

5. **Determine the Most Reactive Element**:
Since Rubidium (Rb) has the highest atomic size and electropositivity among the given elements, it is the most reactive.

**Hint**: Always look for trends in the periodic table when comparing reactivity.

### Conclusion:
Rubidium (Rb) is the most reactive element among Li, Na, K, and Rb.