SCN is thiocyanate ion. IT is not a neutral compound. It has a -1 charge. It is formally written as SCN-. If there are no changes in the system of the solution upon the addition of the SCN-, we can assume that there are no reactions occur. As far as chemistry terms are concerned, there's no such thing as stress ion. Perhaps it would be the ion that reacts with SCN-ion. 

The shift or the direction of the reaction pertains to the formation of the products. If the reaction proceeds to completion, the shift is going to the right. If there are no visible reactions, there is no shifting in the reaction. And if the reactions changes and at some point in time the reaction changes again and stops changing, it is an equilibrium reaction. Equilibrium reaction has an equal shifting (left and right) and it is denoted by a double arrow sign `harr`

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