Final answer:
The correct option is a. 7. Nitrogen, with an atomic number of seven, has two electron shells: two electrons in the first shell and five in the second.
Step-by-step explanation:
The question relates to the atomic structure of nitrogen, which has an atomic number of seven. The atomic structure of nitrogen can be understood by considering its place on the periodic table, and specifically, how electrons are arranged in shells around its nucleus. Since nitrogen has an atomic number of seven, it means that it has seven protons and, when neutral, seven electrons. These electrons are arranged in electron shells based on the principles of electron configurations.
The first shell can hold up to two electrons, and the second can hold up to eight. Given that nitrogen has seven electrons, two will fill the first shell, and the remaining five will be in the second shell. Therefore, nitrogen has two electron shells which makes option b. the correct answer.