The calorific values of petrol and CNG are$45000 \mathrm{kJ}/\mathrm{kg} \mathrm{and} 50,000 \mathrm{kJ}/\mathrm{kg}$, respectively. If you have vehicle which can run on petrol as well as CNG, which fuel will you prefer and why?

 Complete the crossword with the help of the clues:

Across

1. Non-metal which catches fire if exposed to air $\left(10\right)$

3. The lowest temperature at which a substance catches fire is called its _____ temperature. $\left(8\right)$

5. The most common fire extinguisher. $\left(5\right)$

Down

 2. A chemical process in which a substance reacts with oxygen to give off heat. $\left(10\right)$

 4. Petrol is used as a _____ in automobiles. $\left(4\right)$

 6. It is as hard as stone and black in colour. $\left(4\right)$