In a shade scale which amount increases toward the darkest sample?

Correct answer: Black

The governing concept is the difference between tints and shades. A shade is produced by adding black to a hue, thereby lowering its lightness or value. As the scale moves toward the darkest sample, the measured amount of black increases gradually. Therefore option B is correct. White would create lighter tints, water mainly changes transparency in watercolour, and yellow changes hue rather than systematically darkening it.