Question

Why can we not see air even though it is counted as a material and a homogeneous mixture?

Answer 1

Air is a homogeneous mixture of gases such as oxygen, nitrogen, carbon dioxide, water vapour, etc. Since the gas molecules are too small to be visible by naked eye, so we cannot see air. Being homogeneous, we cannot even differentiate between the different gases.
We can only see those materials which can effectively reflect light. Gas molecules bieng very small cannot reflect light.