Final answer:
Sodium (Na) and Chlorine (Cl) are both in the third period of the periodic table, making them the correct pair of elements in the same period. Therefore, the correct option is B.
Step-by-step explanation:
To identify which two elements on the periodic table are in the same period, we must first understand what a period is. A period in the periodic table refers to a horizontal row of elements. Elements in the same period have the same number of atomic orbitals. Now let's look at the pairs of elements provided:
- Hydrogen (H) and Helium (He) are both in the first period.
- Sodium (Na) and Chlorine (Cl) are in the third period.
- Carbon (C) and Oxygen (O) are in the second period.
- Nitrogen (N) and Neon (Ne) are not in the same period; Nitrogen is in the second period, and Neon is in the first period.
Thus, the correct answer to which two elements are in the same period is B) Sodium and Chlorine.