Which of the following in guard cell is responsible for opening of stomata?

1. decrease in $C{O}_{2}$ concentration and more ${H}^{+}$ ion

2. decrease in $C{O}_{2}$ concentration and less ${H}^{+}$ ion concentration

3. increase in $C{O}_{2}$ concentration and more ${H}^{+}$ ion concentration

4. More free ${H}^{+}$ ion and less $C{l}^{-}$ ion.