Question

how is the modern periodic table arranged?
○ by atomic weight, with chemical families or groups in columns and periods in rows
○ by atomic weight, with chemical families or groups in rows and periods in columns
○ by atomic number, with chemical families or groups in columns and periods in rows
○ by atomic number, with chemical families or groups in rows and periods in columns

Explanation:

The modern periodic table corrects the earlier arrangement by atomic weight, organizing elements by increasing atomic number. Vertical columns are groups (chemical families with similar properties), and horizontal rows are periods.

Answer:

by atomic number, with chemical families or groups in columns and periods in rows