Thermit, used in thermit welding, is a mixture of

all of the above

Advantages of thermit welding is listed below:
The weld formed has high mechanical strength, excellent corrosion resistance as compared with other forms of weld.
It is highly stable to repeated short circuit pulses the electrical resistance remains unchanged over lifetime of the installation
All parts of the weld section are molten at the same time Weld cools almost uniformly
Results in a minimum problem with internal residual stresses.

all of the above

Thermit welding is a welding process that employs molten metal to permanently join the conductors.
The process employs an exothermic reaction of a thermite composition to heat the metal, and requires no external source of heat or current.
Thermit welding is often used in Replacing broken gear teeth and Repairing broken shears and Joining rails, truck frames and locomotive frames etc.

vacuum

Electron-beam welding. Electron-beam welding (EBW) is a fusion welding process in which a beam of high-velocity electrons is applied to two materials to be joined.
EBW is often performed under vacuum conditions to prevent dissipation of the electron beam.

liquid form

Acetylene gas is stored in cylinders in liquid form.