Which of the following substances is a weak base?

a. NaOH

b. NH3

c. K2O

d. KOH

b. NH₃.

Explanation:

Firstly, we need to defined the base;

Base is the substance that can produce OH⁻ ions in the solution.

So, NaOH, KOH, and NH₃ are bases because they can produce OH⁻ ions in the solution.

But, K₂O is not a base, it can not produce OH⁻ ions in the solution.

Now, we need to differentiate between strong and weak bases.

Strong bases are bases that can completely ionized in the solution and produce OH⁻ ions.

NaOH and KOH are strong bases because they can completely ionized in the solution and produce OH⁻ ions.

Weak bases are bases that can not completely ionized (ionized partially) in the solution and produce OH⁻ ions.

NH₃is a weak base hat can not completely ionized (ionized partially) in the solution and produce OH⁻ ions.

So, the right choice is: NH₃.