**Core Concept**
The probing pressure applied by the Community Periodontal Index of Treatment Needs (CPITN) probe is used to assess the periodontal status of an individual. This assessment involves measuring the depth of the gingival sulcus or pocket, which is an indicator of periodontal health. The CPITN probe applies a gentle pressure to the gingiva to measure the sulcus depth.

**Why the Correct Answer is Right**
The correct probing pressure applied by the CPITN probe is 0.4-0.5 kg (or 4-5 Newtons). This pressure is gentle enough to avoid causing discomfort or bleeding, while still allowing for an accurate measurement of the gingival sulcus depth. The probe is inserted into the sulcus at a 90-degree angle to the tooth surface, and the depth is measured in millimeters. The probing pressure is critical in ensuring that the measurement is reliable and not influenced by other factors.

**Why Each Wrong Option is Incorrect**
**Option A:** Applying too much pressure can cause bleeding, discomfort, and inaccurate measurements.
**Option B:** Using a probing pressure of 1 kg or more would be excessive and could lead to tissue damage.
**Option C:** A probing pressure of less than 0.2 kg may not be sufficient to accurately measure the gingival sulcus depth.

**Clinical Pearl / High-Yield Fact**
When using the CPITN probe, it's essential to apply gentle pressure to avoid causing discomfort or bleeding, while still ensuring an accurate measurement of the gingival sulcus depth.

**Correct Answer: D. 0.4-0.5 kg**