Explanation:

Transparency: Transparency refers to the property of an object or substance that allows light to pass through it without scattering. In other words, it is the ability of an object or substance to transmit light.

Air: Air is a transparent substance. It is composed of molecules, which are widely spaced and do not scatter light significantly. As a result, we can see through the air easily, and it appears transparent to our eyes.

Fog: Fog is a suspension of small water droplets or ice crystals in the air. These tiny particles scatter and absorb light, making it difficult to see through fog. It appears opaque or translucent, depending on its density. Therefore, fog is not transparent.

Mist: Mist is similar to fog but consists of smaller water droplets. Like fog, mist scatters and absorbs light, causing it to appear opaque or translucent. Hence, mist is not transparent.

Tissue Paper: Tissue paper is a thin, translucent paper often used for wrapping or cleaning purposes. While tissue paper allows light to pass through it, it scatters the light due to its fibrous structure. As a result, objects viewed through tissue paper appear blurred or distorted. Therefore, tissue paper is not transparent.

Conclusion: Among the given options (air, fog, mist, tissue paper), all except air are not transparent. Air is the odd one out as it is the only substance that is transparent.