I believe your answer will be b<span />
The two are potassium and rubidium. Why? Na is an alkali metal. As you go down the metals become more reactive.
Calcium has 20 protons. Why? The atomic # is 20 (the one at the top).
It has 20 neutrons. Why? The atomic mass (the number on the bottom) is ~40, ignoring electron mass. 40- 20 protons = 20 neutrons.
It has 20 electrons.
Why? The # of protons and electrons is the same. Ions aren't on the periodic table.
Please mark brainliest if I helped you!
Answer:
Endocardium
Explanation:
The endocardium makes the innermost lining of the wall of the heart. It is present over the thin layer of connective tissue. The function of the endocardium is to provide a smooth lining for the chambers of the heart. The valves present in the heart also have endocardium. The dense connective tissue of the heart valves is covered by endocardium.
The presence of the smooth endocardium made up of endothelium reduces the surface friction as blood passes through the heart. The endocardium of heart chambers is continuous with the endothelial lining of the large blood vessels that are attached to the heart.
Answer:
The main function of the alveoli is storage of air for a shorter period which permits absorption of oxygen into the blood. The gaseous exchange of oxygen and carbon dioxide typically takes place in the alveoli. The main function of the bronchiole is to allow the passage of air freely into the lungs
