An element X has a mass number 4 and atomic number 2. Write the valency of this element.

Explanation

To determine the valency of the element X with a mass number of 4 and an atomic number of 2, we can follow these steps:

### Step 1: Identify the Element
The atomic number of the element X is 2. This indicates that it has 2 protons. The element with atomic number 2 is Helium (He).

### Step 2: Determine the Electron Configuration
Since the atomic number is 2, the number of electrons in a neutral atom of Helium is also 2. The electron configuration for Helium is:
- K shell: 2 electrons
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