61.
The addition of gypsum to portland cement helps in :

63.
Which of the following is used as a preservative to protect processed food?

64.
Chemical composition of cement is

65.
Which one of the following elements is used in the manufacture of fertilizers ?

66.
Asbestos is formed of :

67.
Bayer's reagent is

68.
Bone ash contains

69.
Cement is made hard with

70.
'Plaster of Paris' is made by partial dehydration of