In a nucleoside,a base is attached at the $1^{\prime}$ position of the sugar moiety. $A$ nucleotide is formed by linking a phosphoric acid unit to the sugar unit of a nucleoside. At which position of the sugar unit is the phosphoric acid linked in a nucleoside to give a nucleotide?

(5') nucleoside consists of a nitrogenous base attached to a pentose sugar at the $1^{\prime}$ position.
When a phosphoric acid molecule is esterified to the hydroxyl group present at the $5^{\prime}$ position of the sugar moiety of a nucleoside,a nucleotide is formed.
Therefore,the phosphoric acid is linked at the $5^{\prime}$ position.