Below are some elements of modern periodic table
`""_4Be , ""_9F, ""_14Si, ""_19K,""_20Ca`
Select the element which has one electron in its outermost shell

Explanation

To determine which element has one electron in its outermost shell, we need to analyze the electronic configurations of the given elements. Here’s a step-by-step solution:

### Step 1: Identify the Elements and Their Atomic Numbers
The elements provided are:
- Be (Beryllium) - Atomic number 4
- F (Fluorine) - Atomic number 9
- Si (Silicon) - Atomic number 14
- K (Potassium) - Atomic number 19
...