When u put a coin in a glass of water, the coins appears to be at a lesser depth than the actual depth of the glass. Which phenomena is responsible for this?

When light travels from water (denser medium) to air (rarer medium), it bends away from the normal due to refraction. This makes the coin appear shallower than its actual position. Reflection involves light bouncing back, buoyancy is about floating, and surface tension is about liquid surface behavior - none of these explain the depth illusion.