Identify, the elements with the following property and arrange them in increasing order of their reactivity.
(a) An element which is a soft and reactive metal.
(b) The metal which is an important constituent of limestone
(c) The metal which exists in liquid state at room temperature.

Explanation

To solve the question, we need to identify three elements based on the given properties and then arrange them in increasing order of their reactivity. Let’s break it down step by step.

### Step 1: Identify the Soft and Reactive Metal
- **Property**: An element which is a soft and reactive metal.
- **Identification**: The alkali metals are known for being soft and highly reactive. Among them, sodium (Na) and potassium (K) are common examples. However, sodium is more commonly referred to as a soft and reactive metal.
- **Element**: Sodium (Na).

### Step 2: Identify the Metal Important in Limestone
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