Question

A mirror or window polished by a dry cloth on a dry day soon becomes dusty

Answer 1

When glass is rubbed with a dry cloth, it removes electrons from the surface of the window causing it to become positively charged; this in turn attracts dust particlesto it - especially on dry days as there is obviously more dry dust about (than when it is humid, as then the window attracts water vapour in the air and soon becomes neutral again!)