The reason that the TLC chamber should be kept closed with a lid on it is Select one:
a. to prevent temperature exchange
b. to prevent decomposition of compounds in the mixture
c. to maintain the gradient of the vapors in the chamber
d. to prevent evaporation of the sovent from the chamber

d. to prevent evaporation of the solvent from the chamber.

Explanation:

TLC or thin layer chromatography is a technique which is used to separate the compounds on the basis of a principal that the different compounds have different solubility and adsorption to the two phases solid and liquid. It is also known as solid liqiud technique in which solid serves as a stationary base and liquid as a mobile phase. Solvent in the chamber should be ina small amount such that a little of bottom part of the plate below the spot should dipped in it. The lid of the chamber should be kept closed to avoid evapouration of solvent.

the total distance traveled by the car is

30km + 49km = 79 km .