Which is a general chemical equation for an endothermic, double-replacement reaction?

Endothermic reaction is the chemical reaction in which energy is absorbed.

And a double displacement reaction is the one in which two elements displaces other elements and exchange places with each other.

So general chemical equation for an endothermic, double-replacement reaction is:  

AB + CD + energy >AD + CB  

Here energy is absorbed so it is an example of endothermic reaction.

While as two elements displaces other elements and exchange places with each other, so it is an example of  double displacement reaction.

Reactant + Heat → Products

Explanation: Hope this helps :)

"the periodic table is arranged in order of atomic number."

the answer to your question is c