For acidic solutions, which element is added to balance half-reactions?
a.
hydrogen
b.
hydroxide
c.
oxygen
d.
nitrogen

We add A Hydrogen

Explanation:

When we have a half-reaction in an acidic media usually we add (H+) hydrogen plus or protons to the reaction to balance in both sides of the reaction the amount of hydrogen.

After this step the next one is equilibrate the charges (e-) and finally we add the two half-reactions to write a short version

a rain shadow is a dry region of land on the side that is protected against the prevailing winds of a mountain range. the prevailing winds are the winds that occur most of the time in a particular place of the earth

prevailing winds carry air toward the mountain range. as the air rises up over a mountain range, the air cools, water vapor condenses, and clouds form. on this side of the mountains, called the windward side, precipitation falls in the form of  rain  or snow. this dry air produces a  rain shadow.

a:

by the combination of an unlimited number of elements