Sodium is more reactive than _____ (`"potassium"//"calcium"`).

Explanation

To solve the question "Sodium is more reactive than _____ (potassium or calcium)," we will refer to the reactivity series of metals. Here’s a step-by-step solution:

### Step 1: Understand the Reactivity Series
The reactivity series is a list of metals arranged in order of decreasing reactivity. The higher a metal is in the series, the more reactive it is compared to those below it.

### Step 2: Identify the Position of Sodium
In the reactivity series, sodium (Na) is positioned above calcium (Ca) and below potassium (K). The order is as follows:
- Potassium (K)
...