1) a / old / yellow / big / contrabass

Correct order of adjectives:

The general order of adjectives in English is: determiner, opinion, size, age, shape, color, origin, material, purpose, noun.

• Determiner: a
• Age: old
• Color: yellow
• Size: big
• Noun: contrabass

Therefore, the correct order is: a big old yellow contrabass.