I think cathode should be silver or gold
you can use silver nitrate solution or mercury nitrate solution
Moles of gas = 0.123
<h3>Further explanation</h3>
In general, the gas equation can be written

where
P = pressure, atm , N/m²
V = volume, liter
n = number of moles
R = gas constant = 0.082 l.atm / mol K (P= atm, v= liter),or 8,314 J/mol K (P=Pa or N/m2, v= m³)
T = temperature, Kelvin
Volume(V) =2.5 L
Pressure(P) = 1.2 atm
Temperature(T) = 25 + 273=298 K

Reactants contact each other, bonds between atoms in the reactants are broken, and atoms rearrange and form new bonds to make the products. Hope this helps!
Answer:
C. Because my teacher said so
Hope this helps :)