Can You Solve this Ice Diamond Riddle? ft. Vsauce’s Michael Stevens

Water level would go down. Explanation: For simplicity, let's assume the diamond has twice the density of water. While floating, a 100g diamond would displace 100g of water. But when it's resting on the bottom of the glass, its weight no longer matters, only its size. And since it's twice as dense as water, it means that 100g of diamond is the same size as only 50g of water. So it will only displace 50g instead of 100g. The water-level will sink.