Largest nuke ever detonated :
Tsar..
50 metatons..
Scaled down version of a 100 mt bomb
Alone,this bomb dropped over France could annihilate 1/8th of his territory and most of Great Britain if detonated over London

!
Holy crap,the soviets dropped the design because it was just too damn powerfull to be used in Europe (warsaw countries were too "close"

)..
http://www.wimp.com/largest/
From Wiki :
Detonated at a altitude of 2 miles,the Tsar Bomba mushroom cloud rose as high as 64 km (40 mi) above the ground.
The fireball touched the ground, reached nearly as high as the altitude of the release plane, and was seen 1,000 km away. The heat could have caused third degree burns at a distance of 100 km. The subsequent mushroom cloud was about 60 km high and 30-40 km wide. The explosion could be seen and felt in Finland, even breaking windows there. Atmospheric focusing
caused blast damage up to 1,000 km away.
Schneider
French-Canadian