To solve this problem, we need to identify the shape of stomata in grass leaves.$\newline$Stomata are small openings on the surface of leaves that allow for gas exchange.$\newline$The shape of stomata can vary among different plant species.$\newline$Let's analyze the options:$\newline \bullet$Option 1: Rectangular - This shape is not typical for stomata in grass leaves.$\newline \bullet$Option 2: Kidney-shaped - This shape is common in dicot plants, not in grasses.$\newline \bullet$Option 3: Dumb-bell shaped - This is the characteristic shape of stomata in grass leaves.$\newline \bullet$Option 4: Barrel-shaped - This shape is not associated with stomata in grass leaves.$\newline$Grass leaves have dumb-bell shaped stomata, which are adapted to their specific environmental conditions.$\newline$Therefore, the correct option is Option 3: Dumb-bell shaped.