Which solution contains Cl, Na, K, Ca, and Mg to maintain heart contractions?

The correct option is Ringer's solution because it is specifically designed to maintain the physiological functions of cells, including those in the heart, by providing essential electrolytes such as chloride (Cl), sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg). These ions play critical roles in cardiac muscle contraction and overall heart function.

Sodium, calcium, and potassium are particularly important in the process of cardiac action potentials and muscle contraction. Calcium ions are crucial for the contraction of cardiac muscle fibers, while sodium and potassium are involved in setting the membrane potential and initiating the action potential.

Normal saline primarily consists of sodium chloride and is not comprehensive enough to provide the range of electrolytes needed for optimal cardiac function. Distilled water lacks electrolytes altogether, making it unsuitable for maintaining heart contractions, as it can lead to dilution of ions and potential cellular dysfunction. Cytoplasm contains various ions and molecules present within cells, but it is not a solution that can be administered externally for maintaining heart contractions as Ringer's solution does.

Overall, Ringer's solution is formulated specifically to replicate the electrolyte composition of body fluids, making it the ideal choice for maintaining heart contractions during physiological studies or medical interventions.