Question

?) Ventilators are usually given at the top of the walls.Why?
?)Freezers is placed at the top of the refrigerators.Why?

Answer 1

ventillators are used at the top of the walls bcz the air coming from the fan pushes the hot air up and is passed through ventillators .freezer are placed at bottom bcz temperature will be more

Answer 2

ventilators are kept at top of the house because in a room the cold air always comes down due to they have more density than warm air so warm air goes up ,so when ventilators are placed up the warm air goes outside.
Freezers are placed at top because,freezer is the source for the refrigerator's coldness. When the freezer is placed on top,the cold air produced from it is denser than the warmer air in the bottom. so cold air being dense sinks down and the warm air is forced to rise up so when the warm air rises up it and gets cold in the freezer