Best option: B

Reasoning: For electrolyte assays an anticoagulant must not contribute extra cations or anions. Lithium heparin is preferred because the lithium ion does not interfere with measurement of the common serum electrolytes (sodium, potassium, chloride, bicarbonate), whereas EDTA contains potassium, citrate contains sodium, and sodium-fluoride tubes contain both sodium and fluoride that can alter results [Tietz, 2015, PMID 25935185].