Answer:
Option A. 2NO + O₂ —> 2NO₂
Step-by-step explanation:
To know which option is correct, it is important that we know what is synthesis reaction.
Synthesis reaction is a reaction in which two different elements or compound combine together to produce a new compound different from the two starting elements or compound. Example of such reaction is given below:
X + Y —> Z
Considering the options given in the question above, only option A comform to the definition of synthesis reaction. Thus, option A gives the correct answer to the question.