$(a)$ What is required in chemical synthesis? What will be done for that?
$(b)$ Write Le Chatelier's principle.

(N/A) One of the principal goals of chemical synthesis is $(i)$ to maximize the products and $(ii)$ to minimize the expenditure of energy.
This implies achieving the maximum yield of products under mild temperature and pressure conditions. If this is not achieved,the experimental conditions must be adjusted. For example,in the Haber process for the synthesis of ammonia from $N_2$ and $H_2$,the choice of experimental conditions is of significant economic importance.
The equilibrium constant,$K_c$,is independent of initial concentrations. However,if a system at equilibrium is subjected to a change in the concentration of one or more of the reacting substances,the system is no longer at equilibrium,and a net reaction occurs in a direction that allows the system to return to equilibrium.
Changes in temperature or pressure of the system may also alter the equilibrium state.
To determine the direction of the reaction and make a qualitative prediction about the effect of changing conditions on equilibrium,Le Chatelier's principle is used.
Le Chatelier's principle: "$A$ change in any of the factors that determine the equilibrium conditions of a system will cause the system to change in such a manner as to reduce or counteract the effect of the change." This principle is applicable to all physical and chemical equilibria.