Question

1. choose the best answer. atomic numbers __ across a period and down the periodic table. increase; decrease decrease; decrease decrease; increase increase; increase 14) choose the best answer. atomic masses across a period and __ down the periodic table. decrease; increase increase; increase increase; decrease decrease; decrease

Explanation:

• For question 13: In the periodic table, as we move across a period (from left to right), the atomic number increases because each element has one more proton than the previous one. As we move down a group (periodic table column), the atomic number also increases since we are adding more electron shells with more protons in the nucleus.
• For question 14: Across a period (left - to - right), the atomic mass generally increases. This is because, although the number of neutrons can vary in a complex way, the overall trend is an increase in the sum of protons and neutrons (which make up atomic mass). Down a group, as we add more electron shells and more protons and neutrons, the atomic mass also increases.

Answer:

1. D. increase; increase
2. B. increase; increase