How to prepare hydrogen by the electrolysis of water ?

Describe the industrial preparation of hydrogen by the electrolysis of water.

Give reason for the following: In the preparation of hydrogen by electrolysis of water - the distilled water used is acidified.

NaOH is prepared by the electrolysis of:

NaOH is prepared by the electrolysis of :

Fluorine is prepared by the electrolysis of

In what ratio by mass, hydrogen and oxygen are produced by the electrolysis of water ?