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

Explanation

There are two elements in the `1^(st)` period and eight elements in the `2^(nd)` period., The third period starts with the element with Z = 11. Now, there are eight elements in the third period. Thus, the `3^(rd)` 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 `17^(th)` group of the third period has atomic number Z = 17.