Order of Adjectives in the Sentence:
The correct order of adjectives in the sentence "The old room on the terrace was musty, unclean, and dark" is as follows:
1. Age (old)
2. Location (on the terrace)
3. Opinion (musty, unclean, dark)
The sentence follows the general rule of adjective order in English, which is:
Opinion - Size - Age - Shape - Color - Origin - Material - Purpose - Noun

Explanation:
- Old: This adjective describes the age of the room, indicating that it is not new but has been around for a while.
- On the terrace: This describes the location of the room, specifying that it is situated on the terrace. Location comes after age in the adjective order.
- Musty, unclean, and dark: These adjectives give opinions about the room. They describe the condition of the room, stating that it is musty (having a stale, moldy smell), unclean (dirty or not well-maintained), and dark (lacking light or brightness). Opinion adjectives typically come at the end of the sequence.
By following the correct order of adjectives, the sentence effectively conveys the description of the old room on the terrace as being musty, unclean, and dark. Each adjective adds a specific detail to paint a vivid picture of the room's unpleasant characteristics.