I can’t see the question :/
        
             
        
        
        
Answer:
676mmHg
Explanation:
Using the formula;
P1/T1 = P2/T2
Where;
P1 = initial pressure (mmHg)
P2 = final pressure (mmHg)
T1 = initial temperature (K)
T2 = final temperature (K)
According to the information provided in this question;
P1 = 725.0mmHg
P2 = ?
T1 = 20°C = 20 + 273 = 293K
T2 = 0°C = 0 + 273 = 273K
Using P1/T1 = P2/T2
725/293 = P2/273
Cross multiply
725 × 273 = 293 × P2
197925 = 293P2
P2 = 197925 ÷ 293
P2 = 676mmHg. 
The resulting pressure is 676mmHg
 
        
             
        
        
        
1.Subscript,how many hydrogen molecules there are 
2.No it is not balanced,oxygen is less than represented.
 
        
                    
             
        
        
        
Answer:
Explanation:
so if the reaction is C2H4+3O2-->2H2O+2CO2
if there were 7 moles of C2H4:
(see the attachment)