no
Depends on whether you say Pluto is a planet or not. If you say it isn't, then there are no planets that haven't been visited by a spacecraft. If you say it is, then there is one that hasn't been visited yet, but one is on the way.
yes, spacecraft have visited Mars, but the results haven't always been positive. More than half of the attempts to send a spacecraft to the planet have failed.
Mars has constantly been visited by spacecrafts. The first spacecraft to visit Mars was the Mariner 4. After that Mars has been visited by numerous spacecrafts like: Mars Pathfinder, Mars Global Surveyor, Mars Odyssey, Mars Express and the Mars 2 which was the first spacecraft to land on Mars.
Pluto has yet to be visited by a spacecraft because it is so far away.
it is too hot at the sun
No its way to hot to even go close to the sun.
No spacecraft has visited all the planets.
Pluto will be visited by the spacecraft New Horizon in 2015
no
voyager 2
Voyager 2 is the only spacecraft to have currently visited both.
yes
Yes
none
Apollo 17
Humans, no. Unmanned spacecraft, yes.