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,:

Answer:
Sn and Ge
Explanation:
To obtain the more metallic element, we compare the group in which both elements are. Generally the element with the lower ionzation energy is he more metallic one.
Ionization energy increases fro left to right across a period. Ionization energy decreases down the group.
1. When comparing the two elements A s and S n , the more metallic element is ______based on periodic trends alone.
Sn has a lower ionization energy so it is the more metallic one.
2. When comparing the two elements G e and S b , the more metallic element is ________ based on periodic trends alone.
Ge has a lower ionizaiton energy compared to Sb. So it is more metallic element than Sb.
Explanation:
A new substance forms with identical properties
Answer:
B. Adding an enzyme to the reaction
D. decreasing the concentration of a reactant.