Myosin head separates from actin when?

Correct option is B. When ATP attached to myosin head. The sliding filament theory explains the mechanism of muscle contraction based on muscle proteins that slide past each other to generate movement. According to the sliding filament theory, the myosin (thick) filaments of muscle fibres slide past the actin (thin) filaments during muscle contraction, while the two groups of filaments remain at a relatively constant length. Myosin has another binding site for ATP at which enzymatic activity hydrolyzes ATP to ADP, releasing an inorganic phosphate molecule and energy. ATP binding causes myosin to release actin, allowing actin and myosin to detach from each other. Hence, Myosin head separates from actin when ATP attached to myosin head. So, the correct answer is 'When ATP attached to myosin head'.