Answer
Two 'H' atoms are attached with the $\alpha$ C of glycine molecule if we see the structure of glycine. so, the C is not chiral in nature. hence, it is not optically active.
Work Step by Step
From the structure of glycine (written below), it is clear that the $\alpha$ Carbon is not chiral in nature because no four different groups are attached to that C atom. One of the main conditions to be optically active for a molecule is that it must have at least one chiral 'C'. So, glycine hasno chiral C in it. Hence, it is optically inactive.
