The chemical name of the principal ore of aluminium is:

1. sodium aluminium fluoride
2. aluminium oxide
3. hydrated aluminium fluoride
4. hydrated aluminium oxide

Brass is an alloy of

1. Copper and tin
2. Copper and zinc
3. Zinc and lead
4. Lead and tin

The reason for using aluminium in the alloy duralumin is

1. Aluminium is brittle.
2. Aluminium gives strength.
3. Aluminium brings lightness.
4. Aluminium lowers melting point.

Duralumin is an alloy with composition:

P — Al and Mg

Q — Al, Cu and Mg

R — Al and Mn

1. Only P

2. Only Q

3. Both P and R

4. Only R