Question

the pH of hydrochloric acid solution is 3. does it mean that it has only hydronium ions. if not, how are OH-ions generated

Answer 1

we know that all acid contain hydronium ions while all base contains hydroxide ions if you want OH-ions generated you :
you do reaction between sodium hydroxide and water it form sodium ion or hydroxide ions OH- ions

Answer 2

For generting OH ions

We can react any base with water

eg:- NaOH + H2O ----> Na+  + OH-