Question

$N{H_4}OH$ is a weak base because:
A. It completely ionized
B. It has low vapour pressure
C. It has low density
D. It is only partially ionized

Answer 1

Base is a substance that in water solution is slippery to the touch, bitter in taste, forms salts in reaction with acid. A base reacts with water to form hydroxide ions by gaining ${H^ + }$ in water.

Complete step-by-step answer: Base are whether strong or not are examined on as
strong bases react completely with water to produce the $O{H^ - }$ whereas weak bases react only partially with water to form hydroxide ions.
When bases react with water they accept ${H^ + }$ ion to form oh ion and more oh ion produced stronger base will.
When a base has a strong bond between its molecules less it will get dissociated and less it will be strong and when a base has weak bonds between its molecules easily it gets dissociated and to form more oh ion and stronger base will.
And $N{H_4}OH$ has a strong bond between its molecules so it is only partially ionized.

So from all above conclusions we can say that option D is the correct option for the question.

Note: A base is whether weak or strong can be safely determined by the pH paper. The increasing $pH$ value of a compound from $7$ to $14$ determines whether a base is strong or weak.
Bases form from alkali metals are the strongest base. Like $NaOH$,$KOH$ etc.