After completing fermentation and extraction, penicillin G is commonly recovered and stabilized as which salt form?

Introduction / Context:
Penicillin G, once produced in broth, is extracted into an organic phase and then re-precipitated as a stable salt. The potassium and sodium salts of penicillin G are widely used pharmaceutical forms, with potassium penicillin G being very common.

Given Data / Assumptions:

• We refer to typical pharmaceutical isolation after fermentation.
• Goal: obtain a stable, crystalline, bioactive salt.

Concept / Approach:
The free acid/base forms of penicillin are unstable. Industrial recovery neutralizes to a pharmaceutically acceptable cation, commonly potassium (penicillin G potassium) or sometimes sodium (penicillin G sodium), depending on product specification. Among the options, potassium penicillin best represents a standard recovered form.

Step-by-Step Solution:

Verification / Alternative check:
Drug compendia list penicillin G potassium and penicillin G sodium as dosage forms. Free penicillin is avoided due to instability.

Why Other Options Are Wrong:

• Calcium penicillin: not a standard for penicillin G pharmaceutical bulk.
• Sodium penicillin “exclusively”: sodium is used, but not exclusively; potassium is very common.
• Free base: unstable; not the normal recovered form.
• Aluminum salt: not used.

Common Pitfalls:
Assuming only one salt is ever used; in practice, both potassium and sodium salts are common—this question asks for a typical recovered form, and potassium penicillin fits well.

Final Answer:
Potassium penicillin (penicillin G potassium)