You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Composition of fixer solution: and explain in detail?
Fixing solution also contains four components, all dissolved in water:  (1) clearing agent, (2) acidifier,  (3) preservative, and (4) hardener.
 
Clearing Agent
An aqueous solution of ammonium thiosulfate (“hypo”) dissolves the unexposed silver halide grains.
 
Acidifier
The fixing solution contains an acetic acid buffer system (pH 4 to 4.5) to keep the fixer pH constant.
 

Preservative
Ammonium sulfite is the preservative in the fixing solution, as it is in the developer.

 
Hardener
A hardening agent, usually aluminum sulfate, complexes with the gelatin during fixing and prevents damage to the gelatin during subsequent handling. 
 
 
 
Reference: White and Pharoah's Oral Radiology Principles and Interpretation 7th edition page no 70