**Core Concept**
The case fatality rate (CFR) is a measure of the severity of a disease, calculated as the number of deaths due to the disease divided by the total number of cases. It is expressed as a percentage and is an important indicator of the disease's virulence and the effectiveness of treatment.

**Why the Correct Answer is Right**
To calculate the CFR of dengue, we need to divide the number of deaths due to dengue (30) by the total number of cases (100). This gives us a CFR of 30/100 = 0.3, which can be expressed as a percentage by multiplying by 100. Therefore, the CFR of dengue is 30%.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not take into account the total number of cases. Without the denominator, the CFR cannot be calculated accurately.
**Option B:** This option is incorrect because it uses the total population of the village (10,000) instead of the total number of dengue cases (100). This would give a misleading CFR.
**Option C:** This option is incorrect because it uses the total number of deaths due to malaria (50) instead of the total number of deaths due to dengue (30). This would give a misleading CFR.

**Clinical Pearl / High-Yield Fact**
The CFR of a disease is an important indicator of its severity and the effectiveness of treatment. It can be used to compare the severity of different diseases and to evaluate the impact of public health interventions.

**Correct Answer: D. 30%**