Question

Read the excerpt from a reading passage titled "Matter and Energy: Evaporation and Condensation." Condensation An example of condensation can be seen when drops of water form on the outside of a glass of ice water. The drops seem to appear from nowhere, but they actually form from water vapor in the air. The dew that forms on grass overnight is another example of condensation. Condensation happens when molecules in a gas cool down. As the molecules lose heat, they lose energy. As a result they slow down. They move closer to other gas molecules. Finally these molecules collect together to form a liquid. (Source: Encyclopaedia Britannica, adapted by Newsela staff, 06/02/2017) Describe the process of how dew forms on a blade of grass.

A. Dew forms on grass as water vapor warms up on blades of grass overnight.
B. Dew forms on grass when water vapor forms when molecules cool and separate.
C. Dew forms on grass when water vapor forms when molecules cool and join together.
D. Dew forms on grass when water vapor forms when liquid cools and becomes a gas.

Answer 1

Answer : The correct option is (C) : Dew forms on grass when water vapor forms when molecules cool and join together.

Explanation :

Air contains a small amount of water vapors. When the temperature of an object is lowered than the ambient temperature, the vapors get condensed and small water droplets are formed on the object.

During night time, when the temperature is lowered, the blades of grass become cool. As a result, the vapor molecules slow down and eventually come close to each other. They join together to form liquid water which gets deposited on the blades in the form of dew drops.

The only option that explains this process is option C.