Why is less atp obtained from a gram of glucose than from a gram of palmitate?

Less ATP obtained from a  gram of glucose that from a gram of palmitate because palmitate contain more carbon atoms that glucose molecule.

Explanation:

Glucose is a 6 carbon compound which  undergo catabolism to generate 2 molecules of acetyl CoA which then then TCA cycle and Electron transport chain to generate 38 molecules of ATP.

               On the other hand palmitate contain 16 carbon atoms which under go breakdown via beta oxidate to generate 8 acetyl CoA along with NADH and FADH2. The later 2 NADH and FADH2 are also formed in TCA cycle .

                  8 acetyl CoA enters in the TCA cycle and the NADH and FADH2 enters ETC or electron transport chain to generate 129 molecules of ATP.