What does the r stand for in the ideal gas law (pv=nrt)?

What semimetal can form four single covalent bonds.

When an object falls through the air and encounters air resistance its overall speed will be than if it had not encountered air resistance? (one word answer)

Although respiratory organs vary across different organisms, they all contain respiratory surfaces that have a large surface area and are extremely thin. explain why having an extremely thin respiratory surface with a large surface area is advantageous for the process of gas exchange