True/False against the following statements and also correct the false statement. 1. A physical process in which a substance reacts with oxygen to give off heat is called combustion. 2. Water is the best extinguisher for fires involving electrical equipment. 3. Alcohol, CNG and LPG are inflammable substances. 4. Increased concentration of nitrogen in the air is believed to cause global warming. 5. Greater the calorific value, the better the fuel. 6. The middle zone is the hottest zone of a flame. 7. The substances, which vaporise during burning, give flame.