A magician during a show makes a glass lens with n = 1.47 disppear in a trough of liquid:-Could the liquid be water?

A magician during a show makes a glass lens with n = 1.47 disppear in a trough of liquid:-What is the refractive index of the liquid?

Calculate the concentration of CO_2" in molL"^(-1) in a soft drink that is bottled with a partial pressure of CO_2 of 4 atm over the liquid at 25^@C. The Henry's law constant for CO_2 in water at 25^@C" is "3.1xx 10^(-2)" mol/litre -atm."

Focal length of a convex lens of refraction Index 1.5 Is 2 cm. The focal length of lens when immersed in a liquid of refractive index of 1.25 will be.