1) Li + H2O = LiOH + H2
We try to get the same number of atoms on both sides of the reaction.
We start with the odd number which is for hydrogen, on the left we have 2, and on the right, we have 3. We try to multiply by a number to get a pair number of atoms.
Here: Li + H2O = 2 LiOH + H2, so we need to multiply by 2 on the left,
Li + 2 H2O =2 LiOH + H2, now we need a 2 next to Li, 2 Li + 2 H2O =2 LiOH + H2
Answer 1): 2 Li + 2 H2O =2 LiOH + H2
We proceed like this for the other ones.
2) 2 Na +2 H2O = 2 NaOH + H2
3) 2 K + 2 H2O = 2 KOH + H2
4) 2 Rb + 2 H2O = 2 RbOH + H2
5) 2 Cs + 2 H2O = 2 CsOH + H2