An element X has four shells and 3 valence electrons. Assign group no. and period no. to it.

Explanation

To solve the question regarding the element X, we need to determine its group number and period number based on the information provided: it has four shells and three valence electrons.

### Step-by-Step Solution:

1. **Identify the number of shells:**
- The element X has four shells. The shells are denoted as K, L, M, and N.
- The number of shells indicates the period of the element. Each shell corresponds to a principal energy level.

...