Maximum number of electrons in an energy shell is given by the formula ........................ .

Explanation

**Step-by-Step Solution:**

1. **Identify the Formula**: The maximum number of electrons in an energy shell is given by the formula \(2n^2\), where \(n\) is the principal quantum number.

2. **Understand the Principal Quantum Number**: The principal quantum number \(n\) represents the energy shell number. It can take positive integer values starting from 1 (i.e., \(n = 1, 2, 3, \ldots\)).

3. **Apply the Formula**: To find the maximum number of electrons in a specific energy shell, substitute the value of \(n\) into the formula \(2n^2\).

...