Answer: Carbon
Explanation: Organic compounds are those made by carbon atoms that link to other carbon or elements such as nitrogen, hydrogen or oxygen with covalent bonds.
The presence of these compounds were associated with living things, because most of them are produced by plants or animals. However nowdays substances like polymers and other synthetically made molecules can also be considered as organic since they are made of carbon.
Two isotopes of the same element will have the same ATOMIC NUMBER but a different MASS NUMBER.
Answer:
a) 
b) 
c) 
Explanation:
Hello,
In this case, in each reaction we must subtract the Gibbs free energy of formation the reactants to the Gibbs free energy of formation of the products considering each species stoichiometric coefficients. In such a way, the Gibbs free energy of formations are:

So we proceed as follows:
a)

b)

c)

Regards.
Independent: Gasoline with different amounts of lead
Dependent: Amount of pollution produced