Final answer:
The word 'Garish' appropriately describes the lurid light against the sky, reflecting an unpleasantly bright, flashy, or showy quality.
Step-by-step explanation:
The word that best describes the lurid light against the sky would be “Garish”.
Based on the given descriptions of the light being “repellent, almost revolting; a smouldering unclean yellow, strange-ly faded by the slow-turning sunlight,” it is clear that the light has an unpleasantly bright and showy quality. Therefore, option b) Garish is appropriate, as it refers to something that is excessively bright, flashy, or showy in a way that is tasteless or unpleasant. Options such as ‘Opale’ (which is not a recognized English word related to color or light), ‘Muted,’ and ‘Subdued’ imply a softness or a toning down that is incompatible with the descriptions provided.