**Core Concept**
The patient's presentation of asymptomatic macules and erythematous painless lesions on the glans, accompanied by generalized lymphadenopathy, is suggestive of primary syphilis. This condition is caused by the bacterium *Treponema pallidum*, which is transmitted through sexual contact.

**Why the Correct Answer is Right**
Benzathine penicillin is the treatment of choice for primary syphilis because it provides long-lasting concentrations of penicillin in the blood, allowing for effective targeting of the treponemes. The recommended dose is 2.4 million units administered intramuscularly, which is usually given in a single dose. This treatment regimen has been shown to be highly effective in curing primary syphilis and preventing its progression to secondary syphilis.

**Why Each Wrong Option is Incorrect**
**Option A:** Ceftriaxone is a cephalosporin antibiotic that is effective against a wide range of bacterial infections, but it is not the preferred treatment for primary syphilis. Ceftriaxone has a shorter half-life than benzathine penicillin and may require more frequent dosing.
**Option C:** Acyclovir is an antiviral medication used to treat herpes simplex virus infections, which can cause similar skin lesions. However, acyclovir is not effective against *Treponema pallidum* and would not be an appropriate treatment for primary syphilis.
**Option D:** Fluconazole is an antifungal medication used to treat fungal infections, such as candidiasis. It is not effective against bacterial infections like primary syphilis and would not be an appropriate treatment choice.

**Clinical Pearl / High-Yield Fact**
It's essential to note that primary syphilis can be asymptomatic, and patients may not present with symptoms until the disease has progressed to secondary syphilis. Therefore, a high index of suspicion and thorough clinical evaluation are necessary to diagnose primary syphilis.

**✓ Correct Answer: B. Benzathine penicillin**