Decantation is a:
A.Process of transferring the clear liquid without disturbing the sediments
B.Process of separating an insoluble solid from a liquid using filter paper
C.Process of settling down heavier, insoluble particles from a mixture
D.Process in which a solid changes directly into the vapour state

Hint: Decantation is basically a separation technique. So, you can go through different separation techniques and can understand what makes decantation different from other techniques.

Complete step by step answer:
We all have experienced that if we leave a bucket full of water mixed with sand or mud undisturbed for a short amount of time most of the insoluble particles settle down at the bottom of the bucket due to the effect of gravity. If we pour the water out by tilting the bucket, settled precipitate will remain at the bottom of the bucket while the relatively clean water can be poured out.
 Decantation is the process of separating insoluble solid particles from a liquid or separating two immiscibles with different densities. More clearly, Decantation is the process where liquid can be separated from sediments or another immiscible liquid with different density manually.
 So, Decantation is the process of transferring the clear liquid without disturbing the sediments. Therefore, option (A) is correct.

Additional Information:
Decantation is a relatively easy process. It can be performed manually. It can easily separate insoluble sediments or immiscible liquids with relative ease.
Disadvantage of the decantation process include that it cannot separate solids or liquids that dissolve in the mixture. For example, it cannot separate salt from water.

Note: Option (b) is also a method of separation but it is not decantation. Because it is separated through a filter paper. Don’t be confused with decantation and filtration. Both are different methods of separation. Option (c) is incorrect because it only allows to sediment but not separating. So, this process is sedimentation and not decantation.