The correct answer is option 'D': Energy can never be stored.

Explanation:
The respiratory balance sheet is a representation of the flow of energy and intermediates through the process of respiration. It shows the utilization of glucose and the production of ATP and other intermediates during cellular respiration. The respiratory balance sheet assumes certain conditions and processes, but it does not assume that energy can never be stored.

Here are the assumptions of the respiratory balance sheet:

a) NADH synthesised in glycolysis is transferred into mitochondria:
This assumption is correct. NADH is a high-energy molecule that is produced during glycolysis, the first step of cellular respiration. The respiratory balance sheet assumes that NADH is transferred into the mitochondria, where it can be further oxidized in the electron transport chain to produce more ATP.

b) None of the intermediates is used to synthesise other compounds:
This assumption is correct. The respiratory balance sheet focuses on the flow of intermediates and energy through the process of respiration. It assumes that none of the intermediates produced during respiration are used for the synthesis of other compounds. Instead, they are primarily used for ATP production.

c) Respiration is a sequential pathway:
This assumption is correct. Respiration is a series of sequential reactions that occur in specific order: glycolysis, the citric acid cycle, and the electron transport chain. The respiratory balance sheet assumes that these reactions occur in a specific sequence and that the intermediates and energy flow through these pathways accordingly.

d) Energy can never be stored:
This assumption is incorrect. Energy can be stored in the form of ATP molecules. ATP is a high-energy molecule that is produced during respiration and can be used by cells as a source of energy. The respiratory balance sheet recognizes the production and utilization of ATP as a key aspect of cellular respiration.

In summary, the incorrect assumption in the respiratory balance sheet is option 'D': Energy can never be stored. Energy can indeed be stored in the form of ATP molecules, which are produced during the process of respiration.