Which generalized equation represents a double displacement reaction?

a. a + bc → ac + b
b. ac +bd → ad + bc
c.ab → a + b

I believe the correct answer from the choices listed above is option B. The generalized equation that represents a double displacement reaction would be  AC +BD → AD + BC. This reaction is a type of chemical reaction where two compounds react, and the positive ions (cation) and the negative ions (anion) of the two reactants switch places, forming two new compounds or products.

Option (B) is the correct answer.

Explanation:

A double displacement reaction is defined as the reaction in which there occurs interchange of both positive and negative ions of the reacting species.

For example,

Here, negative ion that is C and D interchange their places with each other resulting in the formation of two new compounds.

Therefore, we can conclude that the equation is the generalized equation which represents a double displacement reaction.

Answer is: In such conditions, oxygen was available in abundance. 
Because in such conditions there was no or very little oxygen. If there was oxygen the organic matter would not decomposed and formed oil and gas, because there would be reaction of oxidation.
Petroleum is used primarily as a fuel in combustion engines.