Here's why:

* Shell capacity: The maximum number of electrons a shell can hold is determined by the formula 2n², where n is the shell number.

* Fourth shell: For the fourth shell, n = 4.

* Calculation: 2 * 4² = 2 * 16 = 32 electrons.

Important Note: This is the maximum capacity. An atom will only have as many electrons in a shell as needed to fill its orbitals according to the Aufbau principle and Hund's rule.