**Core Concept**
Syphilis is a sexually transmitted infection (STI) caused by the bacterium Treponema pallidum. The disease progresses through distinct stages: primary (chancre formation), secondary (hematogenous dissemination), and tertiary (organ damage).

**Why the Correct Answer is Right**
The primary stage of syphilis is characterized by the formation of a painless chancre at the site of infection, typically on the genitals. This is due to the localized immune response to the bacteria. The painlessness of the chancre is a key distinguishing feature from other genital ulcers. The painless nature of the chancre is also why it often goes unnoticed, leading to delayed diagnosis and potential transmission to others.

**Why Each Wrong Option is Incorrect**
**Option A:** The incubation period of syphilis is indeed 9-90 days, which is a wide range due to the variable time it takes for the body to mount an immune response.

**Option B:** Secondary syphilis is indeed due to hematogenous dissemination of the bacteria, where the infection spreads through the bloodstream to other parts of the body.

**Option D:** General paresis of the insane, also known as general paralysis of the insane (GPI), is a rare but serious complication of tertiary syphilis, where the infection damages the central nervous system (CNS) and can lead to dementia and other cognitive impairments.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the chancre in primary syphilis is typically painless, which is a key diagnostic feature that differentiates it from other genital ulcers. This is a critical point to remember for accurate diagnosis and treatment of syphilis.

**✓ Correct Answer: C. Syphilitic ulcers(Chancre) are extremely painful**