Why is it that during changing weather, one is advised to avoid closed, crowded and air conditioned places like cinema halls, etc.?

A wet porous subtance in the open air loses its moisture at a rate proportional to the moisture content. If a sheet hung in the wind loses half its moisture during the first hour, then the time when it would have lost 99.9% of its moisture is (weather conditions remaining same)

Why ozone is used for purifying air in crowded places such as cinema halls, underground railway stations, tunnels etc. ?

Deep sea divers have been using the compressed air containing N_2 in addition to O_2 for breathing. When the sea divers breathes in compressed air at a depth, more N_2 dissolves in the blood and other body fluids than would dissolved at the surface because the pressure at the depth is far greater than surface atmospherice p ressure. when the diver comes towards the surface, the pressure decreases and N_2 comes out of the body quickly forming bubbles in the stream which restrict blood flow and affect the transmission of nerve impuses. this results into a condition called 'the bends' which is dangerous and painful. To avoid this condition, professionals now use air diluted with helium. As a student of chemistry, can you analyse as to why helium is used?

In a household electric circuit, different appliances are connected in parallel to one another. Give two reasons An electrician puts a fuse of rating 5A in that part of domestic electrical circuit in which an electrical heater of rating 1.5 kW, 220V is operating. What is likely to happen in this case and why? What change, if any, needs to be made?

Diseases like dysentry, cholera, typhoid, etc. are more common in over-crowded human settlements. Why?