Classification of respondents only on the basis of gender is an application of

Answer: Option B

Understanding Scales of Measurement:
In statistics, we use different scales to measure data. Think of it like measuring things with different rulers.

Nominal Scale: This is like labeling things with names. We just give them categories without any order or ranking.
Example: Colors (red, blue, green), Gender (male, female), Types of cars (sedan, SUV, truck).

Ordinal Scale: This scale has order or ranking, but the difference between each rank isn't necessarily equal.
Example: Education level (high school, bachelor's, master's), Customer satisfaction (very satisfied, satisfied, neutral, dissatisfied, very dissatisfied).

Interval Scale: Here, the difference between each point is equal, but there's no true zero point.
Example: Temperature in Celsius or Fahrenheit (0°C doesn't mean there's no temperature).

Ratio Scale: This scale has equal intervals and a true zero point. Zero means the absence of the thing being measured.
Example: Height, weight, age, income.

Applying it to the Question:
The question asks about classifying respondents by gender (male, female). We're just assigning labels, not ranking or measuring anything numerically. Therefore, this is a nominal scale.

Therefore, the correct answer is B: Nominal scale