Question

1. choose the best answer.

atomic numbers __ across a period and __ down the periodic table.
decrease; decrease
decrease; increase
increase; decrease
increase; increase

1. choose the best answer.

a ____ of elements is also known as a group.
triad
column
block
row

Explanation:

• For question 11: In the periodic table, as we move across a period (from left - to - right), the atomic number increases because we are adding protons (and electrons in a neutral atom). As we move down a group (periodic table column), the atomic number also increases because we are moving to elements with more electron shells and more protons.
• For question 12: In the periodic table, a column of elements is called a group. A triad is a set of three related elements (an old concept). A block refers to groups of elements based on their electron - filling (e.g., s - block, p - block). A row is called a period.

Answer:

1. increase; increase
2. column