Question

What is black when you buy it, red when you use it, and gray when you throw it away?

Answer 1

coal is the answer of your question

Answer 2

$\textbf{\large{Answer -}}$

What is black when you buy it, red when you use it, and gray when you throw it away?

$\textbf{Charcoal}$ is black when we buy it, red when we use it and Gray when we throw it away.

Usually the colour of charcoal is black.

When we burn it, it turns red.

After it turns to ash, the colour is grey and then we throw it.