An "International Unit" of penicillin activity established in 1944 is amount of penicillin equivalent to

• 0.6 micrograms of crystalline penicillin G of about 98% purity
• 0.6 micrograms of crystalline penicillin F of about 98% purity
• 0.8 micrograms of crystalline penicillin G of about 98% purity
• 0.8 micrograms of crystalline penicillin G of about 90% purity