Which of the following compound is optically inactive?

The correct option is A Propanoic acid

Molecules that posses chirality are optically active. Chiral carbon is the one having all different groups attached.

Propanoic acid is: $C{H}_{3}C{H}_{2}COOH$ has no chirality thus its optically inactive

Glyceraldehyde:$HOCCH\left(OH\right)C{H}_{2}OH$ has a ciral center thus its optically active

Lactic acid is $H_{3}CCH\left(OH\right)COOH$ has a chiral center thus its optically active

Glucose is $HOCCH\left(OH\right)CH\left(OH\right)CH\left(OH\right)CH\left(OH\right)C{H}_{2}OH$ has multiple chiral center thus its optically active

thus option A is correct