Which of the following has the largest atomic radius ?

$\text{A}l=13\text{p},13{\text{e}}^{-},\text{Si}=14\text{p},14{\text{e}}^{-},\text{C}l=17\text{p},17{\text{e}}^{-},\text{Na}=11\text{p},11{\text{e}}^{-}$

All the given elements belongs to 3^rd period.  In a period atomic radius decreases from left to right.  Hence  $\text{Na}>\text{A}l>\text{Si}>\text{C}l$.  Na has large atomic radius.