What is the maximum number of electrons that can be present in an atom in which the highest principal quantum number is 4 ?

Explanation

To determine the maximum number of electrons that can be present in an atom with the highest principal quantum number (n) equal to 4, we can follow these steps:

### Step 1: Understand Principal Quantum Number
The principal quantum number (n) indicates the energy level of an electron in an atom. The value of n can be any positive integer (1, 2, 3, ...). In this case, the highest principal quantum number is 4.

### Step 2: Identify Possible Subshells
For n = 4, the possible subshells are:
- s (l = 0)
...