The Modern Periodic Table has 18 vertical columns known as ‘groups’ and ______ horizontal rows known as ‘periods’.
Show answer & explanation
Correct answer: A
Explanation
The correct answer is Option 1 i.e. 7.
The Modern Periodic Table has 18 vertical columns known as 'groups' and 7 horizontal rows known as 'periods'. Each group contains elements with similar chemical properties due to having the same number of valence electrons. Each period represents the principal energy level or shell in which electrons are found, with elements in the same period having the same number of electron shells.