What is reactivity series? How does the reactivity series of metals help in predicting the relative activities of various metals?

Explanation

### Step-by-Step Solution

1. **Definition of Reactivity Series**:
The reactivity series is an arrangement of metals in order of their reactivity, from the most reactive to the least reactive. This series helps in understanding how different metals will react in various chemical situations.

2. **Order of Reactivity**:
The metals are arranged in decreasing order of their reactivity. For example, the reactivity series includes metals such as potassium, sodium, calcium, magnesium, aluminum, zinc, iron, lead, hydrogen, silver, and gold. The metals at the top of the series are more reactive than those at the bottom.

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