27) C

REMEMBER: From the equation c = ƒ x λ, we know speed is directly proportional to wavelength.

Speed of light in glass is 2/3 that of speed of light in air.
Hence, wavelength of light in glass will also be 2/3 that of wavelength of light in air.

Similarly, speed of light in water is 3/4 times that of speed of light in air.
Hence, wavelength of light in water will also be 3/4 times that of wavelength of light in air.

Wavelength of the ray of light in water = 360 nm (Given)
To calculate the wavelength of light in air, we need to divide 360 by 3/4.
Wavelength of the ray of light in air = 360 ÷ (3/4) = 360 x (4/3) = 480nm

Wavelength of light in glass is 2/3 that of wavelength of light in air.
Wavelength of light in glass = 2/3 x 480 = 320nm

Hence, C is the answer.