Answer: 
Explanation: A double displacement reaction is one in which exchange of ions take place.
The compounds which are soluble in water are designated by symbol (aq) and those which are insoluble in water and remain in solid form are represented by (s) after their chemical formulas.
Thus the exchange of ions take place and all the compounds are soluble so the chemical formulas are followed by the symbol (aq).
When you ride a bicycle, several things happen that require energy and it's transformation. You pedaling the bike is transforming chemical energy, supplied by the breakdown of the food you eat, into mechanical energy to turn the pedals. The chemical energy is potential and the mechanical energy is kinetic.
Answer:
I think the layers of the atmosphere does temperature increase with increasing height. It is affected by convection because it heats the lower atmosphere. It is affected by conduction because the is the transfer of thermal energy. I guess
Hope this help!
Answer: The missing coefficient is 2.
Explanation:
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.

As in the products, there are 2 atoms of sodium, thus there will be 2 atoms of of sodium in the reactant as well. This will balance the number of hydrogen and oxygen atoms as well.
Thus the missing coefficient is 2.