The purity of orange made from red and yellow pigments mainly depends on what?

Correct answer: On pigment bias and cleanliness

Pigment purity depends largely on the colours already present in the chosen red and yellow and on whether the tools and mixtures are clean. Each pigment may have a bias toward another hue; unwanted blue or violet bias can neutralise part of the mixture and make the orange dull or brownish. Option B is correct. Paper size, brush length and a painted border do not determine the chemical or visual purity of the mixture, though clean tools are essential for preventing contamination.