Answer:
Speed of light decreases when it goes from a rarer medium to denser medium and increases when it travels from denser to rarer.
Explanation:
when light will fall on aquarium the glass wall and water inside it are denser compared to the air outside. so, the ray will refract from its original path (bending towards the normal) and decrease its speed. The reverse happens when it travels out of aquarium. the air is less dense compared to the water and glass so it will increase the speed.
