Pm2.5 in cloudy weather

A, the unit obtained by 2.5μm× 10-6m does not exist. This option is wrong;

b、c、d、∵ 1μm= 10-6m= 10-5dm= 10-4cm,∴2.5μm=2.5× 10-6m=2.5× 10-5dm=2.5× 10-4cm.

So choose B.