Did you guys use Celsius or Fahrenheit?

Probably doesn’t matter. The nuke was hotter than a blue flame, yielding 4,000 degrees Celsius. A blue flame is about 1,650 degrees Celsius.

I don't know

It could’ve been higher. I saw a few places say Little Boy was 1,000,000 degrees Celsius, so Fat Man couldn’t have been far off from that.

Depends on what is the best form of temperature.

The actual temperature can vary, but for part 2: Yes.

Any nuclear bomb will be hotter than a blue flame. This is because what forms from a nuclear blast is not fire, but rather plasma, which is astronomically hotter than fire.

If you cannot visualize it, just think of the sun: a giant ball of plasma.

Thank you, guys. I'm not really good with science.

During the first few seconds the surface temperature of the fireball was about 7,700 C. At the core, however, the temperature was closer to 100,000,000 C, about 7 times hotter than the core of the sun (15,000,000 C). It quickly cooled as the fireball expanded

BTW that's why you have to use a fission weapon ("A-Bomb") to set off a fusion bomb ("H-Bomb"). It takes temperatures near 100,000,000 C to fuse protons (hydrogen) to make helium because protons are positively charged and repel each other. The force of the repulsion between two protons is huge! It's on the order of about 30 kg (70 lbs).