This colour is NOT a primary colour in the Munsell color system:

Correct option is D

The Munsell color system is a scientifically designed color classification model created by Albert H. Munsell in the early 20th century. It categorizes colors based on three attributes: hue (type of color), value (lightness), and chroma (intensity). Unlike traditional color models like RGB (Red, Green, Blue) or CMY (Cyan, Magenta, Yellow), the Munsell system defines five primary hues that are equally spaced to create a perceptually uniform color wheel.
The five primary hues in the Munsell system are:
• Red (R)
• Yellow (Y)
• Green (G)
• Blue (B)
• Purple (P)
Information Booster: The Munsell Color System & Primary Hues
The Munsell color system was designed to match human visual perception rather than follow the traditional color theories used in paint mixing or digital displays. It defines color in a three-dimensional model:
1. Hue – The type of color (e.g., Red, Green, Yellow, etc.).
2. Value – The lightness or darkness of the color, measured from black (0) to white (10).
3. Chroma – The intensity or purity of a color, with higher chroma meaning more vivid colors.
The five primary hues of the Munsell system are equally spaced to create a perceptually balanced model. Unlike the RYB (Red, Yellow, Blue) model used in traditional painting or the RGB (Red, Green, Blue) system in digital screens, the Munsell model is based on visual uniformity, meaning colors are spaced according to how humans perceive differences in color.
Since Orange is not one of the five primary hues, it is considered a secondary or intermediate hue, positioned between Red and Yellow in the Munsell system.
Additional Knowledge: Explanation of Incorrect Options
(a) Yellow: Yellow is a primary hue in the Munsell system. It is positioned between Red and Green and is one of the five fundamental hues used to define all other colors in this model.
(b) Green: Green is also a primary hue in Munsell’s system. Unlike in the RYB model (used in art) where it is a secondary color, Munsell considers Green as a primary hue.
(c) Purple: Purple is one of the five primary hues in the Munsell model. It is different from spectral Violet, which appears in the visible light spectrum. Munsell’s Purple is a mix of Red and Blue, designed based on human perception.
Each of these incorrect options is a primary hue in the Munsell system, while Orange is not.