Which of the following is a noble metal?

Give reasons for the following:
$(i)$ Alloys are used in electrical heating devices rather than pure metals.
$(ii)$ Gold ornaments look new even after several years of use.
$(iii)$ An iron grill should be painted frequently.

Generally,metals are solid in nature. Which one of the following metals is found in liquid state at room temperature?

Which of the following metals is soft enough to be cut easily with a knife?

Which of the following gases is combustible?

From amongst the metals sodium,calcium,aluminium,copper and magnesium,name the metal:
$(i)$ which reacts with water only on boiling,and
$(ii)$ another which does not react even with steam.