Ans. is 'a' i.e. 10% formalin o 10% formalin is used as preservative for histopathological examination of tissue but not used for poisoning or chemical analysis.Preservatives for specific poisons1. Saturated sodium chloride: In all cases of poisoning excluding corrosive acids, except carbolic acids (phenol), alkalis, corrosive sublimate and aconite.2. 30 mg potassium oxalate (anticoagulant) and 10 ml sodium fluoride (enzyme inhibitor) : Blood in suspected poisoning including alcohol but excluding oxalic acid, ethylene glycol, fluoride, carbon monoxide.3. Rectified spirit : All except in cases of poisoning by : (i) phenol, phosphorus, paraldehyde, (ii) kerosene, (iii) formaldehyde, formic acid, (iv) alcohol, acetic acid (v) chloroform, chloral hydrate, (vi) ether.4. 10 mg/ml Na/K. fluride and 3 mg K-oxalate: For preserving blood; fluride is also added to CSF, vitreous humor; and urine if alcohol estimation is required; and also in analysis of cocaine, cyanide and carbon monoxide.5. 5% (w/v) sodium citrate and 0.25% (v/v) formalin: Blood grouping.6. 30 mg sodium citrate in place of potassium oxalate: Blood in poisoning of oxalic acid and ethylene glycol.7. 10 gm sodium nitrite in place of sodium fluoride: Blood in poisoning by fluoride.8. Heparin and EDTA: Not used as interfere with methanol detection.9. 10% formalin: Histopathological examination of tissue but not used for poisoning or chemical analysis.10. Liquid paraffin : In CO poisoning added immediately over blood to avoid atmospheric O2 exposure.11. Thymol, cone HCL, sodium fluride, saturated saline, rectified sprit, sodium benzoate and toluene : Urine (10 ml).12. 50% glycerine : Specimen for virological examination.13. No preservative: (i) Bone, hair, nail (ii) lung for detecting inhaled poison, (iii) refrigration available (4degC), (iv) analysis within 24 hours.