A lake surface is exposed to an atmosphere where the temperature is less than `0^(@)C`, if the thickness of the ice layer formed on the surface grows from 2 cm to 4 cm in 1 hour, the atomospheric temperature will be
(Thermal conductivity of ice, `K = 4 xx 10^(-3) cal cm^(-1) s^(-1) .^(@)C^(-1)` density of ice `= 0.9 g "cc"^(-1)`. Latent of density during of the state change. Assume that the water below the ice has `0^(@)C` temperature every where.)

Options

A. `-20^(@)C`
B. `0^(@)C`
C. `-30^(@)C`
D. `-15^(@)C`

Answer

C