The freezing point would be 3.72 *C
Use PV =nRT. Rearrange it to n = PV/RT.
P = 202.6 kPa
V = 4.0L
R = 8.314 kPa*L/mol*K
T = 127 °C + 273 = 400 K
Plug it in and solve. I got 0.24 moles of H2.
Mass C₂H₂ needed : 22.165 g
<h3>Further explanation</h3>
Reaction
2C₂H₂+
5O₂ ⇒ 4CO₂ + 2H₂O
75.0 grams of CO₂ , mol CO₂ (MW=44 g/mol) :

mol C₂H₂ :

mass C₂H₂ (MW=26 g/mol) :
