Acetylene is used in-
Illumination of cycle lamps, hawker's lamps and buoys in light houses.
Producing oxyacetylene flame for welding and cutting.

When ethyne is burnt in air incomplete burning takes place and produce sooty flame due to limited supply oxygen present in the air.

Acetylene may be prepared using Kolbes electrolytic method employing potassium fumerate. Acetylene is obtained at anode. The solution is basic due to formation of KOH at cathode.
$\displaystyle  (CHCOONa) _2 \xrightarrow {Electrolysis} C _2H _2+2CO _2+2KOH + H _2$

Reaction: $CH \equiv CH \xrightarrow{Na} Na - C \equiv  CH \xrightarrow{C _2H _5I} C _2H _5 - C \equiv  CH + NaI$

$H-\overset{Br}{\overset{|}{\underset{Br}{\underset{|}{C}}}}-\overset{Br}{\overset{|}{\underset{Br}{\underset{|}{C}}}}-H\xrightarrow[\triangle]{2n}H-C\underset{(A)}{\equiv} C-H\xrightarrow{ red hot \ tube} C _6H _6$

Reaction of process:
$CH\equiv CH+2NaNH _2\rightarrow NaC\equiv CNa\xrightarrow {2 mole CH _3I} CH _3CH\equiv CHCH _3$

This is dehalogenation process:

When carbide reacts with cold water, the by-product formed is calcium hydroxide.

The chemical reaction can be shows as follows which indicates the formation of acetylene
$CaC _2(s) + 2H _2O(l) \rightarrow C _2 H _2(g) + Ca(OH) _2 (g)$

Ethyne is used for the production of oxy-acetylene flame for welding and cutting metals.

Only $2[CH _3] \xrightarrow[\Delta]{Ag} HC \equiv CH$ give acetylene

The hydrogenation of acetylene can be written as:
$C _{2}H _{2} + 2H _{2} \rightarrow C _{2}H _{6}$
As 2 moles of hydrogen are required to saturate one mole of acetylene and 1 mole = 2g of $H _{2}$, therefore 4g of hydrogen are required to saturate one mole of acetylene .

Dehydrobromination is an organic reaction in which alkyl halide when boiled with alc.alkali gives corresponding alkene called as beta-elimination reaction.