Which of the following metals will react with water to produce a metal hydroxide and hydrogen gas?

a. K

b. Sn

c. Ni

d. Mn

The answer would be: K

Kalium or Potassium is one of the metal that located in the first column of the periodic table. It was a strong base with one valence. If react with water it would have an equation:

2K + 2H2O = 2KOH + H2

The kalium hydroxide will form ion if put on the aqueous state. It will become K + and OH-, thus increasing the water pH.