Answer:
Blank 1: 4
Blank 2: 1
Blank 3: 2
Step-by-step explanation:
The unbalanced reaction expression is given as: 
 Na + O₂ → Na₂O 
Now, we use a mathematical approach to balance the reaction given above. 
Assign coefficients a , b and c for the blanks:
 aNa + bO₂ → cNa₂O 
Conserving Na : a = 2c 
 O: 2b = c 
So, let c = 1, a = 2 and b = 
 
 
 Multiply through by 2; 
 a = 4, b = 1 and c = 2
  4Na + O₂ → 2Na₂O 
Blank 1: 4
Blank 2: 1
Blank 3: 2