- A speck is a kind of solid object
- Color is a kind of physical / visual property
- So, specks of different colors are different substances

- The statement "Vibrating matter can produce sound" is irrelevant

- Specks of different colors are different substances
- A powder is made up of white specks and black specks
- So, the powder is made up two different substances

- The powder is made up two different substances
- An mixture is formed by two or more substances combined together physically
- Therefore, the powder is a mixture

So, the powder is a mixture
Question
A powder made up of both white specks and black specks is likely to be

Context
- An mixture is formed by two or more substances combined together physically 
- A speck is a kind of solid object 
- Vibrating matter can produce sound
- A powder is made up of white specks and black specks 
- Color is a kind of physical / visual property