Which Liquid Requires More Volume to Conceal a Coin: Oil or Water?

[jakey]

Question on total reflection...if you were to conceal a coin, by putting it under a beaker whose lid is covered with foil, and you slowly add a liquid until the coin seemingly disappears, which would require a greater volume? oil or water?

 

[Volcano]

Do you mean a coin in dip of a pool? If it is, answer is oil for the same color of light. When light cross to air(minor indice) will far a way from normal. Thus come closer to distinctive surface. Much flux of indice, much far a way from normal.