Well, sort of. Blackpowder is the original mixture of sulfur, charcoal and saltpeter, though the manufacturing process has greatly improved. Gun powder is a more generic term for the various mixtures...
In some countries it may be marketed as such. Although cocao power is only the low fat component of chocolate, so it is likely that chocolate powder has added 'goodness' such as sugar.
No, two totally different substances. First of all hot cocoa mixes contain sugar, powdered milk, salt, and cocoa powder and possibly some other ingredients. But cocoa powder is pure and is not any...