Answer: 
Explanation
Combustion is a chemical reaction in which hydrocarbons are burnt in the presence of oxygen to give carbon dioxide and water.
According to the law of conservation of mass, mass can neither be created nor be destroyed. Thus the mass of products has to be equal to the mass of reactants. The number of atoms of each element has to be same on reactant and product side. Thus chemical equations are balanced.
The balanced combustion reaction for butane is,:

The answer is b. as a whole, the species is mutually beneficial to carry on each others traits and exist in the same ecosystem.
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Decreasing the temperature of the reaction,the reaction shifts forward.
The explanation is given below.
Explanation:
If the temperature of the reaction mixture is increased,then the equilibrium will shift to decrease the temperature.
If the temperature of the reaction mixture is decreased,then the equilibrium will shift to increase the temperature.
During the formation of the ammonia,it gives off heat.So it is an exothermic reaction.
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A decrease in the temperature favors the reaction that is exothermic (the forward reaction)because it produces energy.Therefore,if the temperature is decreased,the yield of the ammonia increases.
<em>Therefore if the temperature is increased,the reaction shifts forward and the yield of the ammonia increases and it is an exothermic reaction.</em>