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 an element indicates the number of protons in its nucleus. For element X, the atomic number is 2, which corresponds to the element Helium (He).

### Step 2: Determine the Electron Configuration
The atomic number also tells us the number of electrons in a neutral atom. Since Helium has an atomic number of 2, it has 2 electrons. The electron configuration for Helium is 1s², meaning both electrons occupy the first energy level (the s subshell).

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