Question

Atomic radius (pm) of Al, Si, N and F respectively is:
A.117,143, 64, 74
B.143, 117, 74, 64
C.143, 47, 64, 74
D.64, 74, 117, 143

Answer 1

Atomic radius generally measures the size of the atom. Atomic radius is usually the mean or typical distance from the center of the nucleus to the boundary of the surrounding shells of electrons.

Complete answer:
Atomic radius is the distance of the nucleus to the outermost shell of an atom. It is generally defined as van der waals, ionic and covalent radius. On moving across the period atomic radius decreases this decrease can be explained on the basis of screening effect which increased due to effective nuclear charge. On moving down the group atomic radius increases as the number of shells increases so atomic size and atomic radius also increases.
Hence we say that atomic radius of fluorine is less than nitrogen as fluorine takes place after the nitrogen and trend says moving across left to right atomic radii decreases. Similarly the atomic radius of Si is less than Al. The atomic radii of Si and Al is higher than that of N and F because Si and Al are third period elements while N and F are second period elements so in Si and Al electron shells are higher as compared to N and F.

Thus option B is the correct answer.

Note:
Atomic radius is measured by distance between the nuclei of two different atoms that barely touch each other. The diameter of the distance between the two nuclei is divided by two to get the radius.