How to determine the strong base and weak base?

The ##K_b## determines if a compound is a weak base or a strong base.

A strong base dissociates completely in solution (has a ##K_b ≫ 1##).

A weak base dissociates slightly in solution (has a ##K_b ≪ 1##).

A base can be a strong base, even if it contributes only a few ions to the solution.

Thus, ##"NaOH"## is a strong base because it dissociates completely:

##"NaOH(aq)" → "Na"^+"(aq)" + "OH"^"-""(aq)"##

If you dissolve ##10^"-8" color(white)(l) "mol of NaOH"## in 1 L of water, it will contribute only ##10^"-8"color(white)(l) "mol"## of ##"OH"^"-"## ions, but that is 100 % of what it has to give.

##"NaOH"## is a strong base. Its strength does not depend on its concentration.