Write the atomic number of the element present in the third period and a seventeenth group of the periodic table.
There are two elements in the 1st period and eight elements in the 2nd period., The third period starts with the element with Z = 11. Now, there are eight elements in the third period. Thus, the 3rd period ends with the element with Z = 18 i.e., the element in the 18th group of the third period has Z = 18. Hence, the element in the 17th group of the third period has atomic number Z = 17.
The element is chlorine (Cl) with atomic number (Z) = 17.
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