About 
553.6
 grams of oxygen are used in this combustion.
Explanation:
Molecular mass of acetylene: 
2
⋅
M
M
C
+
2
⋅
M
M
H
M
M
C
 = Molecular mass of carbon
M
M
H
 = Molecular mass of hydrogen
So, 
2
⋅
12
+
2
⋅
1
=
26
 grams/mole
Mass used in combustion
molecular mass
=
moles used in combustion
180
 grams
26
 grams
mole
=
6.92
 moles
According to the main equation, to 2 moles of acetylene, 5 moles of oxygen are used. 
M
M
O
=
2
⋅
16
=
32
grams/mole
So, if we use 
6.92
 moles of Acetylene, 
x
 moles of oxygen will be necessary.
x
=
6.92
⋅
5
2
=
3.46
⋅
5
=
17.3
 moles of oxygen.
17.3
moles
⋅
32
grams
mole
=
553.6
 grams of oxygen