Vaporization and Production of bubbles. Production of heat and melting are physical changes
Because it contains hydrogen which isn't formed by a special process like oxygen
Answer:
The correct answer is option D.
Explanation:
Step 1: 
Step 2: 
Overall reaction can be determined by adding all the reactions of mechanism:

Reactants in an overall reaction = 
Products in an overall reaction = 
According to question , the role of oxygen gas is product.
Answer:
PRESSURE is right answer .
Explanation: