Answer:
 FAD substitution will produce 28 ATP instead of 36.
Explanation:
NAD and FAD are coenzymes involved in reversible oxidation and reduction reactions. These compounds are also known as electron carriers. However NADH produce 3 electrons in electron transport chain and FADH2 produce 2 electron beacuase it transfer the electrons to second complex in ETC.
Normal prduction of ATP from glucose;
2 cytoplasmic NADH formed in glycolysis         Each yields 2 ATP  	+4
2 NADH formed in the oxidation of pyruvate	Each yields 3 ATP         +6
2 FADH2 formed in the citric acid cycle         Each yields 2 ATP         +4
6 NADH formed in the citric acid cycle             Each yields 3 ATP         +18
2 ATP from glycolysis                                                                                   +2  
2 ATP from citric acid cycle                                                                          +2                             
                                                                     Net yield ATP	+36
C6H12O6 + 6 CO2 + 36 ADP + 36 Pi ⇒6 CO2 + 6 H2O + 36 ATP	
If we replace the NAD with FAD the total ATP production would be.
2 cytoplasmic FADH2 formed in glycolysis          Each yields 2 ATP            +4
2 FADH2 formed in the oxidation of pyruvate   Each yields 3 ATP    +4
2 FADH2 formed in the citric acid cycle            Each yields 2 ATP    +4
6 FADH2 formed in the citric acid cycle                  Each yields 2 ATP   +12
2 ATP from glycolysis                                                                                    
+2
2 ATP from citric acid cycle                                                                            +2
                                                                   <u>Net yield ATP	+28</u>
C6H12O6 + 6 CO2 + 28ADP + 28 Pi ⇒6 CO2 + 6 H2O + 28 ATP