How many electrons can the first shell of an atom contain?

The first shell of an atom can indeed hold a maximum of two electrons. This is determined by the principles of quantum mechanics and the way electrons are arranged in atomic structures. The first shell corresponds to the principal quantum number n=1, where the maximum number of electrons is calculated using the formula 2n². In this case, when n=1, the formula yields 2(1)² = 2.

Therefore, the first shell can only accommodate two electrons, which helps create stable electron configurations in lighter elements. This is significant as it establishes the foundation for how atoms bond and form molecules, influencing the chemical properties of elements.

The other choices reflect the capacities of additional shells or energy levels beyond the first. For instance, the second shell can hold up to eight electrons, while the third shell can hold up to 18. Understanding these limits is essential for grasping atomic structure and behavior.