Which of the following has the smallest atomic
radius?
gest
1. si
2. al
3. s
4. p
5. cl

Cl

Explanation:

Cl have smallest atomic radius because,

As we move from left to right across the periodic table the number of valance electrons in an atom increase. The atomic size tend to decrease in same period of periodic table because the electrons are added with in the same shell. When the electron are added, at the same time protons are also added in the nucleus. The positive charge is going to increase and this charge is greater in effect than the charge of electrons. This effect lead to the greater nuclear attraction. The electrons are pull towards the nucleus and valance shell get closer to the nucleus. As a result of this greater nuclear attraction atomic radius decreases. In given list of elements all are present in period three. Chlorine is present at the  most right side of periodic table so it has smaller radius and Al in on left side it has greater radius as compared to the elements given in question.

"the periodic table is arranged in order of atomic number."