Ajar is filled with water, and the lid is closed tightly. the jar is kept at constant temperature. what happens at the surface of the water? a. water molecules evaporate and condense at the same rate. b. water molecules evaporate and condense, but evaporation occurs more quickly. c. water molecules evaporate only and do not condense. d. water molecules condense only and do not evaporate.

Here we have to choose the correct statement which will be applicable to a jar fill of water kept in a constant temperature.

The surface of the water molecules evaporate and condense at the same rate.

Evaporation of water ⇆ condensation of water.

The rate of evaporation will increase if the outside temperature is more as the evaporation of water started at elevated temperature. The jar is kept in constant temperature thus this statement is not valid.

If the water molecules only evaporate or only condense that will violate the rule of constant mass, which is not possible.

Thus the rate of evaporation and condensation will be same for the water at the surface.  

c-14 is carbon-14, or radiocarbon.   it is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons.