From hydrogen, sodium, zinc and argon select
Element which produces a gas on reacting with water.

Explanation

To solve the question of which element produces a gas when reacting with water from the options provided (hydrogen, sodium, zinc, and argon), we can follow these steps:

### Step 1: Identify the Elements
We have four elements to consider:
- Hydrogen (H)
- Sodium (Na)
- Zinc (Zn)
- Argon (Ar)
...