Question

Three elements 'X', 'Y' and 'Z' have atomic numbers $7,8,$ and $9$, respectively. Arrange these elements in the decreasing order of their atomic radii.

Answer 1

Three elements 'X', 'Y' and 'Z' having atomic numbers 7, 8 and 9 are nitrogen, oxygen and fluorine respectively. The atomic size decreases from left to right in a period in the modern periodic table. Hence, the decreasing order of their atomic radii is $N>O>F$.