5. We use the zero conditional when we have absolute certainty of the statement (facts
and general truths). For example if you take an ice cube and put it in the sun it
melts. If it did not, you would think there was something very wrong with the
world.
We use the zero conditional when we are thinking of a simple fact. It is not past,
present or future, it simply is. But it must be a fact that always remains the same
no matter what. When can substitute if for when in the zero conditional, but the
meaning doesn’t change.

8. We use the first conditional to talk about a possibility in the future.
There needs to be a real possibility that this situation could occur.
Although we are thinking about a possibility in the future, the
condition is always presented in the present simple, and the result is
presented with “will + the base verb”.
I will go out tonight even if it rains.

11. Like the first conditional we are thinking about the future, however with the second
conditional, the situation is unreal, or unlikely to occur (hypothetical). For example you
could be thinking what you would do if you had a lot of money or were a millionaire.
Most of us aren’t millionaires, but we like to think what we would do if we were. It’s like
a dream.
We use the past simple in the second conditional and most commonly “would + base verb”
in the result. However, if there is less certainty in your statement or if something is
possible, but you might choose not to do it, then use “could or might + base verb”.
The use of “could” indicates that there is the possibility or ability to buy a house in
London, but it’s not certain that you would follow the action. It is like saying you could