A 26 year old male with recent history of unprotected sexual intercourse comes to opd with complaints of painless, indurated ulcer over the glans which exuded clear serum. Bilateral painless inguinal lymphadenopathy is also present. The most appropriate diagnostic test is:

**Core Concept**
The patient's symptoms are indicative of a sexually transmitted infection (STI) characterized by a painless, indurated ulcer and bilateral painless inguinal lymphadenopathy, which is a classic presentation of primary syphilis.

**Why the Correct Answer is Right**
The diagnosis of primary syphilis is confirmed by a serological test, specifically the Venereal Disease Research Laboratory (VDRL) test or the Rapid Plasma Reagin (RPR) test. These tests detect the presence of non-treponemal antibodies, which are produced in response to the infection. A positive result on one of these tests is a strong indication of syphilis, and further confirmation can be obtained through a treponemal test, such as the Treponema pallidum haemagglutination assay (TPHA) or the Fluorescent Treponemal Antibody Absorption (FTA-ABS) test.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not specified, so we cannot evaluate it.
**Option B:** This option is not specified, so we cannot evaluate it.
**Option C:** This option is not specified, so we cannot evaluate it.
**Option D:** This option is not specified, so we cannot evaluate it.

**Clinical Pearl / High-Yield Fact**
It is essential to note that syphilis can be asymptomatic in its early stages, and the only way to diagnose it is through serological testing. A high index of suspicion is necessary, especially in patients with a history of unprotected sexual intercourse.

**Correct Answer: A. VDRL test**

✓ Correct Answer: C. Dark ground microscopy of ulcer discharge