31.
Which of the following is not a method of preparing oxygen?

32.
Which one of the following statements is not correct? Vulcanisation of rubber makes it

33.
The compounds formed when hydrogen combines with p-block elements are called

34.
In vulcanisation process, rubber can be hardened by adding

35.
The substance that is added to make natural rubber strong and more bouncy is

36.
In arc welding, Argon is used because of its

37.
An inert gas mixed with oxygen given to patients suffering from restricted breathing is

38.
Which of the following elements is obtained from seaweeds ?

39.
Silica gel is a