Arrange the metals K, Na and Ca in decreasing order of reactivity on the basis of reaction with water.

Explanation

To arrange the metals Potassium (K), Sodium (Na), and Calcium (Ca) in decreasing order of reactivity based on their reactions with water, we can follow these steps:

### Step 1: Understand the reactions of each metal with water.
- **Potassium (K)**: When potassium reacts with water, it forms potassium hydroxide (KOH) and hydrogen gas (H2). This reaction is very vigorous.
- **Sodium (Na)**: Sodium also reacts with water to form sodium hydroxide (NaOH) and hydrogen gas (H2). This reaction is vigorous but less so than potassium.
- **Calcium (Ca)**: Calcium reacts with water to produce calcium hydroxide (Ca(OH)2) and hydrogen gas (H2). This reaction is fast but not as vigorous as the reactions of potassium and sodium.

### Step 2: Compare the vigor of the reactions.
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