The part of atmosphere which is rich in ozone may be called ozone layer, ozonosphere, ozone umbrella or ozone shield. In 1985, Farman found that ozone layer had thinned out over Antarctica. It was called on ozone hole.
A similar but smaller hole was also found over arctic region by Augestein (1987). Atmospheric ozone is measured by spectrometer and is expressed in Dobson Units (DU).
The correct option is B.