Arrange the following solutions in order of increasing hydroxide ion concentration (lowest to highest):
a buffer solution with a pH of 11.0
0.5 M HCl
0.1 M HNO3
a solution of HNO2 with a pH of 4.0
water

0.5 M HCl lowest hydroxide ion concentration

0.1 M HNO3

HNO2 with a pH of 4.0

Water

A buffer solution with a pH of 11.0highest hydroxide ion concentration

Explanation:

A solution with higher number of hydrogen ions  is acidic thus has a low pH value.A solution with high number of hydroxide ions is basic thus has high value of pH.A buffer solution are those used to resist the change in the pH value of a solution when small amounts of strong acid or strong base are added.The pH value of pure water is 7 , however the normal value for pH in surface water is 6.5 to 8.5.

altitude, density, pressure

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

atomic number of carbon is 6

electronic configuration of carbon is 1s²2s²2p²

orbital diagram of carbon is as shown here in the image.