A sample of a molecular substance starting as a gas at 206°C and 1 atm is allowed to cool for 16 minutes. Determine the number of minutes that the substance was in the liquid phase, only.

i think that the answer is c

c) should be the answer.

answer: semi-infinite solid initially at a uniform temperature of 400 ◦c is cooled at its surface by convection. the cooling fluid at a constant temperature of 200 ◦c has a convective coefficient (ha) of 250 w/m2.k. the physical properties of the solid: k = 20 w/m.k and α = 4 * 10-5  m2/s. using δx = 0.04 m and δt = 10 s. write the finite difference equations describing the transient heat transfer of the first five δx and the temperature profile after 30 s.