Question

State one relevant observation for each of the following reaction:
Action of dilute hydrochloric acid on iron (II) sulphide.

Answer 1

Reactants: The compounds which react with each other to form a new compound, are known as reactants.
Products: The compounds which are formed when reactants react with each other, are known as products.

Complete step by step solution:
Here we have to find the product when dilute hydrochloric acid reacts with iron (II) sulphide. Iron (II) sulphide is the compound having molecular formula $FeS$ (because in this compound the oxidation number of iron is $2$) and the molecular formula of hydrochloric acid is as $HCl$.
The reaction is as follows:
$FeS + 2HCl \to FeC{l_2} + {H_2}S \uparrow$.
The products formed are as $FeC{l_2}$ which is known as ferric chloride and ${H_2}S$ which is known as hydrogen sulphide and the arrow which is pointing upwards represents that the compound ${H_2}S$ is gaseous.
Additional information:
Generally the compound whose oxidation number increases during the reaction is known as oxidised compound and the compound whose oxidation number decreases during the reaction is known as reduced compound.
Now let us first talk about the oxidations number of elements in the compounds given in the reaction.
Oxidation number of an element: It is defined as the total number of electrons that an atom accepts or loses in order to make a chemical bond which results in the formation of a chemical compound.
Here in the question the products are ferric chloride and hydrogen sulphide in which the oxidation number of iron is $2$ because the oxidation number of chlorine is $- 1$. And the oxidation number of sulphur in hydrogen sulphide is $- 2$ because the oxidation of hydrogen is $+ 1$.
Oxidation: The compound which loses the electron during the reaction or the compound whose oxidation number increases during the reaction.
Reduction: The compound which gains the electron during the reaction or the compound whose oxidation number decreases during the reaction.

Note:
Another way of defining oxidised and reduced compounds are as follows:
Oxidized compound: The compound to which oxygen is added during the reaction, is known as oxidized compound.
Reduced compound: The compound from which oxygen is removed during the reaction, is known as reduced compound.