Find the odd word from the given alternative.

Milk tastes sour when kept in the open for sometimes due to the formation of-

The nucleus of an atom consists of-

The most reactive among the halogens is-

Formation of ozone hole is maximum over

The most reactive among the halogens is-

The gas usually causing explosions in coal mines is-

The pH of a neutral solution is — 

Petroleum is a mixture of-

The absolute value of the charge on electron was determined by-

The acid used in lead storage cells is-