Question

Lithium and fluorine belong to ______ of the modern periodic table.

• A. 4th group
• B. 2nd period
• C. 5th period
• D. 2nd group

Answer 1

The correct option is B 2nd period

The atomic number of lithium and flourine are 3 and 9 respectively.

Lithium has 2 electrons in the first shell and 1 electron in the second shell.

Since the number of valence electrons is one, lithium belongs to first group.
Since a lithium atom has two shells, it belongs to second period.

Flourine has 2 electrons in the first shell and 7 electrons in the second shell.

Since the number of valence electrons is seven, fluorine belongs to group 17.
Since a fluorine atom has two shells, it belongs to second period.

Both fluorine and lithium belong to second period.