Complete the followings reaction and balance it:
(A).\[KMn{{O}_{4(s)}}+HC{{L}_{(l)}}\to \]
(B).$N{{a}_{2}}S{{O}_{3(s)}}+HC{{l}_{(aq)}}\to $
(C).$C{{a}_{3}}{{P}_{2(s)}}+HC{{l}_{(aq)}}\to $

Hint: To solve this question we should have prior knowledge about how hydrochloric acid reacts with the given compounds. And to balance a chemical reaction we should write all the products and bi products which are formed after the reaction.

Complete answer:
The first reaction is the reaction of \[KMn{{O}_{4(s)}}+HC{{L}_{(l)}}\].
The chemical reaction will be:
\[KMn{{O}_{4(s)}}+HC{{l}_{(l)}}\to KCl+MnC{{l}_{2}}+{{H}_{2}}O+C{{l}_{2}}\]
This means that potassium permanganate reacts with hydrochloric acid and produces potassium chloride and manganese chloride along with water and chlorine as the product of the reaction.
The balanced chemical reaction of potassium permanganate with hydrochloric acid is:
 \[2KMn{{O}_{4(s)}}+16HC{{l}_{(l)}}\to 2KCl+2MnC{{l}_{2}}+5{{H}_{2}}O+8C{{l}_{2}}\]
The second reaction is the reaction of $N{{a}_{2}}S{{O}_{3(s)}}+HC{{l}_{(aq)}}$
The chemical reaction will be:
$N{{a}_{2}}S{{O}_{3(s)}}+HC{{l}_{(aq)}}\to Nacl+S{{O}_{2}}+{{H}_{2}}O$
This means that sodium sulfite reacts with hydrochloric acid and produces sodium chloride and sulphur dioxide and water molecules as the product of the reaction.
The balanced chemical reaction of sodium sulfite with hydrochloric acid is:
$N{{a}_{2}}S{{O}_{3(s)}}+2HC{{l}_{(aq)}}\to 2Nacl+S{{O}_{2}}+{{H}_{2}}O$
The third reaction is the reaction of $C{{a}_{3}}{{P}_{2(s)}}+HC{{l}_{(aq)}}$
The chemical reaction will be:
$C{{a}_{3}}{{P}_{2(s)}}+HC{{l}_{(aq)}}\to CaC{{l}_{2}}+P{{H}_{3}}$
This means that calcium phosphide reacts with hydrochloric acid and produces calcium chloride and phosphine as the product of the reaction.
The balanced chemical reaction between calcium phosphide and hydrochloric acid is :
$C{{a}_{3}}{{P}_{2(s)}}+6HC{{l}_{(aq)}}\to 3CaC{{l}_{2}}+2P{{H}_{3}}$

Note:
Balancing a chemical equation means that we add stoichiometric coefficient to the products and to the reactants. The balancing of a chemical reaction is important because any chemical equation must follow the law of constant proportion and the law of the conservation of mass which means that there should be the same number of atoms in both the reactants as well as the product side.