As the elements in period 2 of the periodic table are considered in succession from left to right, there is a decrease in atomic radius with increasing atomic number. this may best be explained by the fact that the
a. number of protons increases, and the number of shells of electrons remains the same
b. number of protons increases, and the number of shells of electrons increases
c. number of protons decreases, and the number of shells of electrons remains the same
d. number of protons decreases, and the number of shells of electrons increases

A. number of protons increases, and the number of shells of electrons

remains the same.

Explanation:

The number of protons increases as you go from left to right in a period. That increases the number of positive charges in the nucleus. The number of negatively charged electrons in the last shell also increases but the number of shells remains the same. The increasingly positive nuclear charge attracts the increasingly negative shells. The result is the atomic radius decreases as the atomic number increases in a period.

altitude, density, pressure

air gets less dense the higher the altitude and also the air pressure is less as altitude rises.