During the formation of a tornado,

cool air condenses

warm air evaporates

cool and warm air sink

cool and warm air meet

Answer: Option (4)

Explanation: For the formation of a tornado, warm air must meet the cold air.

Initially, the warm air present in the lower atmosphere, gets heated up, being less dense, rises up and mixes up with the cold and denser air mass present in the upper atmosphere. Due to this collision of both the air masses, and the presence of water vapor, it gets converted into water droplets and formation of clouds. With time a more intense funnel forms due to the wind from all direction and forms a tornado.

Thus, the correct answer is option (4).

The very last option is the correct answer.