_________ paper is used to check the presence of moisture in the air.
The correct option is D Cobalt chloride
Cobalt chloride paper is used to check the presence of moisture. When dry, the paper is blue in colour. When the humidity increases, then the paper turns pink.
This paper has several applications. Some of them are:
1) In bell jar experiment, it is used to give a visual proof of water loss/transpiration.
2) It is used to check the leakage of water through tiny cracks in pipes.