If the molarity of a solution of ammonium carbonate, (NH4)2CO3 is 0.50M, the molarity of ammonium ion, NH4+, is A) 0.50
B) 1.0
C) 0.25
D) 2.0

what is the question here. i think you messed up.

the correct answer would be b) volume versus temperature, because they are also directly proportional.

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.