Which number in the hydrologic cycle diagram represents precipitation? a) 1

b) 2

c) 3

d) 4
PS. I think I know the answer but I just wanted to make sure

See explanation

Explanation:

A redox reaction is one in which there is a loss and gain of electrons. This means that a specie looses electrons and other species gain electrons.

This loss and gain of electrons ultimately result in a change in oxidation number of chemical species from left to right in the reaction equation.

Now let us look at the specific case that we are considering;

2Ca(s) + O2(g) >2CaO(s)

We can see that the change in oxidation number of calcium from left to right is 0 to +2 while the change in the oxidation number of oxygen from left to right is 0 to -2.

Hence calcium is oxidized and oxygen is reduced. This is a redox reaction indeed!