In a chemical reaction, when a more reactive metal displaces the less reactive metal from its salt solution, it is called displacement reaction, e.g. zinc can displace copper from its copper sulphate solution as zinc is more reactive than copper. Less reactive metal cannot displace the more reactive metal from its salt solution, e.g. copper cannot displace zinc from its zinc sulphate solution as copper is less reactive than zinc.

Some food stuffs which have acidic nature such as citrus fruits, lemon pickles and curd should not be stored in container made up of metals such as copper, zinc, aluminium and iron. This is because acid present in food stuffs reacts with these metals to produce toxic compounds which cause food poisoning.

No, we cannot store lemon pickle in aluminium utensil because aluminium is a metal and lemon contains acid. The acid reacts with metal to give hydrogen and salt. This salt is toxic in nature which will spoil the food and makes it unfit to use
Citric acid + Aluminium \(\rightarrow \) Aluminium salt + Hydrogen \(\uparrow \)
(From lemon)                      (Toxic)

Non-metals do not react with water.

No, displacement reaction does not take place because copper is less reactive than zinc.

(i) Nitrogen
(ii) Phosphorus

Take about 50 mL of water in a beaker and dissolve 5 g of copper sulphate in it to obtain copper sulphate solution (which is blue in colour). Put a clean iron nail in this solution and keep the beaker undisturbed for sometime.
We will find that the blue colour of copper sulphate solution starts fading gradually and the iron nail gets covered with a red-brown layer of copper metal. It is because iron is more reactive than copper, so it displaces copper metal from its solution of copper sulphate. It is the copper metal set free from its compound which forms a red-brown layer on the surface of iron nail. This shows that iron is more reactive than copper.
Copper sulphate + Iron\(\rightarrow \) Iron sulphate + Copper
(Blue solution)      (Grey) (Greenish solution) (Red-brown)