Select the correct passive form of the given sentence.

  Swallows build new nests every year.

The important ore of aluminium is-

An electric iron has a heating element made of:

Formation of ozone hole is maximum over

The gas used for filling weather balloons is-

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

The important ore of aluminium is-

Which one amongst the following is not a Green House gas?

A polymeric substance used to make parachute is

The acid used in lead storage cells is-

 Alum stops bleeding in minor cuts because of