Lithium has an atomic number of 3 and a mass number of 7.
Which of the following is the number of protons in a lithium atom?

Calcium ions play a crucial role in initiating muscle contraction.

When a muscle cell is stimulated to contract by an action potential, calcium channels open in the sarcoplasmic membrane and release calcium into the sarcoplasm.

Some of this calcium attaches to troponin, which causes it to change shape. This shape change exposes binding sites for myosin on the actin filaments.

Myosin’s binding to actin causes cross-bridge formation, and muscle contraction begins.

The other ions mentioned in the question do not have this specific role in muscle contraction.

Potassium ions are important for maintaining the resting membrane potential of cells, but they do not bind to the troponin complex.

Phosphorus ions are important for energy metabolism but do not bind to the troponin complex.

Sodium ions are important for generating action potentials but do not bind to the troponin complex.

The polarity of water molecules explains its solvent abilities for certain substances.

Water is a polar molecule because it has a partial positive charge on one end and a partial negative charge on the other end due to the unequal sharing of electrons between the oxygen and hydrogen atoms.

This polarity allows water to dissolve other polar substances and ionic compounds.

Choice A. Kinetic energy of liquid water molecules is not the correct answer because kinetic energy refers to the energy of motion and does not directly explain water’s solvent abilities.

Choice B. High specific heat is not the correct answer because specific heat refers to the amount of heat required to raise the temperature of a substance and does not directly explain water’s solvent abilities.

Choice C. High surface tension is not the correct answer because surface tension refers to the cohesive forces between liquid molecules and does not directly explain water’s solvent abilities.