Which of the following is a noble metal?

Reaction between $X$ and $Y$ forms compound $Z$. $X$ loses an electron and $Y$ gains an electron. Which of the following properties is not shown by $Z$?

Generally,when metals are treated with mineral acids,hydrogen gas is liberated,but when metals (except $Mn$ and $Mg$) are treated with $HNO_3$,hydrogen is not liberated. Why?

Give a reason why electrical wires are coated with plastic.

Which of the following metals exist in their native state in nature?
$(i)$ $Au$
$(ii)$ $Cu$
$(iii)$ $Ag$
$(iv)$ $Fe$

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.