Ncert Exercises & Solutions

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

There are two elements in the 1 $^{s t}$ period and eight elements in the 2 $^{n d}$ period. The third

period starts with the element with Z = 11. Now, there are eight elements in the third

period. Thus, the 3 $^{r d}$ 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.