The correct answer is A. Ethanol.

This photo depicts gouty tophi. Tissue should be fixed in absolute ethanol (or Carnoy’s fluid) to preserve urate crystals.

Formalin, used for routine histology processing, largely dissolves the urate crystals.

Glutaraldehyde is used for fixation of tissues for electron microscopy, not for gouty tophi.

Michel’s transport medium is used for fixation of tissue for direct immunofluorescence.

While normal saline could be used in place of Michel’s medium for DIF for a short duration (<24 hrs), it is not preferred.

References:

Chabra I, Singh R. Gouty tophi on the ear: a review. Cutis. 2013 Oct;92(4):190-2. PMID: 24195091.