Nitric acid is a potent oxidizing agent. It reacts with hydrogen to form water. Due to this, when a metal is treated with nitric acid, hydrogen gas is not liberated.

Compound X is iron oxide Fe₂O₃ . This reaction is called thermite reaction. This reaction is given by following equation:

2 Al  + Fe₂O₃ → 2Fe  +Al₂O₃  + heat

X is sodium because molar mass of NaOH is 40; which can be shown as follows:

Na (23) + O(16) + H (1) = 40

So, Y is NaOH

Z is hydrogen gas which easily catches fire.

Reaction between sodium and water can be given as follows:

2Na + 2H₂O → 2 NaOH + H₂

X is carbon. Diamond and graphite are allotropes of carbon. Diamond is the hardest natural substance and hence Y is diamond. Graphite is a good conductor of electricity and hence Z is graphite.

The following reaction takes place when aluminium powder is heated with MnO₂

3MnO₂(s) + 4Al(s) → 3Mn(l) +2Al₂O₃  + Heat

(a) Is aluminium getting reduced?

(b) Is  MnO₂ getting oxidised?

Ans. In this reaction, aluminium is getting oxidized because oxygen gets combined to it. Since oxygen is removed from manganese dioxide hence MnO₂ is getting reduced.

Lead and tin are the constituents of solder alloy. Solder alloy has a low melting point; which makes it suitable for welding electrical wires.

Metal A is aluminium and B is Al₂O₃ .

Reaction of aluminium oxide with HCl:

Al₂O₃ + HCl → 2AlCl₃ + 3H₂O

Reaction of aluminium oxide with NaOH: 

Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O

This metal is mercury because mercury exists as liquid at room temperature. Mercury ore is called cinnabar (HgS). When cinnabar is heated in presence of air, following reaction takes place: 

2HgS + O₂ → 2 HgO + 2 SO₂

Mercury oxide is further heated to obtain mercury:

2HgO → 2Hg + O₂