Rigor mortis rigor mortis is due to the loss of acetylcholine receptors at the neuromuscular junctions is independent of environmental factors occurs as the sarcoplasmic reticulum deteriorates, releasing calcium ions involves appendicular skeletal muscles only

Rigor mortis occurs as the sarcoplasmic reticulum deteriorates, releasing calcium ions.

Rigor mortis, also known as postmortem rigidity is the post mortem state caused by chemical changes in the muscles that results in the stiffens of the limbs. It is the third stage of death which appears about 4 hours post mortem.

b is the best answer for this question.