A mixture of which one of the following pairs of gases is the cause of occurrence of most of the explosions in mines?

Which one of the following is used as an explosive?

Which one of the following is not an explosive :

'Nobel oil' is the name of which one of the following explosives?

Which of the following is the procedure for a biogas plant?

To avoid ‘knocking’ of the engine of a car, which one of the following is used as an anti-knocking agent?