First, guns do not kill people - they are inanimate objects. Probably the most common firearm, and due to commonality, likely to be used in more shootings, is the .22 rimfire.
Overall, based on sheer numbers produced and the intended audience, the AK family of automatic assault rifles likely kills the most people world-wide. The AK family is generally chambered for one of two calibers: the 7.62x39 or 5.45x39, with the 7.62x39 being far more common (about 10:1 in numbers).
If one is talking only about murders and other deaths in a civilian setting (not wartime or other settings), then the most common would likely be one of: 7.62x39 (AK family), 9mmx19 Parabellum (most handguns), or the .40 S&W (majority of police handguns). Note that, world-wide, suicides and gun accidents make up the majority of gun-related deaths in a civilian setting, with murders and police shootings coming in well below either of them.
Train
Atleast 5 a year most from heat exhaustion
About 7 million people visit the Ranworth broad each year. The Ranworth broad is the second most visited place in the United States of America. It is located in Norfolk village and very popular in spring and summer.
There are not billions of people in the US but it is still the 3rd most populated country in the world. The population of the US is about 306 million as of 2009. China and India each have more than 1 billion people.
1
House fly
That's a very difficult question to answer because, of course, any caliber can kill. Smaller caliber handguns are fairly common in crime involving handguns because people believe large handguns are too diffucult to conceal. Most major police agencies in the U.S. use 9mm or .40 caliber handguns. It's also difficult to answer because information on caliber used in homicide and other crimes isn't readily available.
Pneumonic Plague, if not treated within the first 24 - 48 hours of infection, the mortality rate is 100%. If it is, the mortality rate is 75%.
Of all the larger land animals of Africa, the hippo is the most dangerous and kills a number of humans each year.
the mosquitoe
cancer
I can say that i shot a fine Antelope buck with my 270Win caliber rifle at 403 paces in Wyoming.I have seen this caliber make many kills from that distance on in to 35 yards.It all depends on the game animal hunted,and most important your rifle skills.
Overall, lighitng kills the most people, though tornadoes are not far behind.
is it cocaine or tobacco The answer above is incorrect, as cocaine is not legal and tobacco is not a drug. Alcohol is most likely the answer to your question, it is legal and also kills thousands of people each year, some of which were not even using the drug... but were victims of the effects the alcohol had on the person who killed them.
the thing is there is a different amount every year so there is no real answer
deer
the most harmful disease in the world is cancer (it kills the most people).