Write the atomic number of the element present in the third period and seventeenth group of the periodic table.

🔍 Step-by-step:

• Third period elements range from atomic number 11 (Na) to 18 (Ar).

• Group 17 elements are the halogens, with general outer configuration: ns² np⁵.

• The Group 17 element in the third period is Chlorine (Cl).

✅ Answer:

The atomic number of the element in the third period and group 17 is:
17 (Chlorine)