Octet means presence of a total of 8 electrons in its valence shell while in case of duplet only 2 electrons are present in valence shell.
Given question is incomplete. The complete question is as follows.
Balance the following equation:

Answer: The balanced chemical equation is as follows.

Explanation:
When a chemical equation contains same number of atoms on both reactant and product side then this equation is known as balanced equation.
For example, 
Number of atoms on reactant side:
H = 5
P = 1
O = 6
Ca = 1
Number of atoms on product side:
H = 6
P = 2
O = 9
Ca = 1
In order to balance this equation, we will multiply
by 2 on reactant side and we will multiply
by 2 on product side. Hence, the balanced chemical equation is as follows.

Answer:
the top of the roller coaster
Explanation:
the roller coaster at the top when it has the most potential energy reaches Peak when its going to convert into kinetic energy
Answer:
Decomposition
Explanation:
If we look at the process;
2 NaHCO3 (s) → Na2CO3 (s) + H2O (g) + CO2 (g)
We can see that NaHCO3 was broken down into Na2CO3, H2O and CO2.
The breakdown of one compound to yield other chemical compounds is known as decomposition.
Hence the NaHCO3 was decomposed in the process above.