Life Processes: Respiration, Circulation and Excretion

Directions: Read the following information and answer the given question.

Raman had his first day at gym today. He had exercised hard over there for the first time. After reaching home he realised his calves are paining. His mother advised him to take rest and not to get worried as he had got cramps. Raman followed his mother's advice.

Which of the following substances is accumulated in muscles during cramps formation?