You (get/will get) water if you (will mix/mix) hydrogen and oxygen.
get, mix
If it (was/is) very cloudy, it (is/isn't) hard to see the sun.
is, is
If you (will be/are) in the sun for a long time, it (is/will be) bad for your skin.
are, is
If the weather (was/is) good, people (go/goes) out more.
is, go
If it (rained/rains) from time to time, it (is/isn't) good for plants and trees.
rains, is
When the sun (will go/goes) down, it (gets/got) dark.
goes, gets
If you (heat/will heat) water at the top of Mount Everest, it (boils/boiled) at 71°C.
heat, boils
If you (put/puts) ice in the sun, it (will melt/melts).
put, melts
If you (press/will press) this button, the computer (turned/turns) off.
press, turns
Tea (taste/tastes) sweet if you (will add/add) some sugar.
tastes, add