16. The presence or absence of oxygen in the materials may result in the

a. Changes in the materials

b. materials remain the same

17. Iron, nails, cans and other metals with iron when exposed to moisture may
develop

a. dust

b. rust

18. The process of burning materials with the aid of oxygen is

a. conduction

b. combustion
19. The reaction of iron with moisture and oxygen present in the air is called

a. rusting

b. cleansing

20. The absence of oxygen in lightning a candle will cause the candle's flame
a. ignite

b. extinguish​