Which statement best describes the relationship between an element's position in a period and its number of valence electrons?

• A. The number of valence electrons remains constant as you move across a period.
• B. As you move across a period from left to right, the number of valence electrons decreases.
• C. All elements in a period have the same number of valence electrons.
• D. As you move across a period from left to right, the number of valence electrons increases.

Answer: (D)

Verified step by step guidance

1. Recall that a period in the periodic table is a horizontal row of elements.
2. Understand that the number of valence electrons corresponds to the electrons in the outermost shell of an atom, which largely determines chemical properties.
3. Recognize that as you move from left to right across a period, each successive element has one more proton and one more electron than the previous element.
4. Since electrons fill the outer shell progressively across a period, the number of valence electrons increases by one for each element moving left to right.
5. Therefore, the relationship is that the number of valence electrons increases as you move across a period from left to right.