Misc: the 'purple heart' medal was created in 1668, 1701 or 1782?

Questions

[science and technology] what is the lightest known gas?

[science and technology] what is the unit used to measure supersonic speed?

[science and technology] what do the initials NASA of the us government agency for space flight represent?

[science and technology] what is a chuckwalla?

[science and technology] how many pockets has a snooker table?