PART - 1 CH - 2 Acids, Bases and Salts — Science STD 10 — Question

Strong base: The base which is ionised completely when dissolved in water is called strong base. For example, sodium hydroxide (NaOH), potassium hydroxide (KOH).
$\rightarrow$ In an aqueous basic solution, total solute substance is in the form $OH ^{-}$ions because of its complete ionisation, i.e., the total solute substance is ionised in the form of $OH ^{-}$.
For example,

Thus, in $1 M~ Mg ( OH )_2$ aqueous solution, the concentrations of $Mg ^{2+}$ and $OH ^{-}$are 1 M and 2 M respectively. Thus, by ionisation of 1 mole $Mg ( OH )_2, 2$ moles $OH ^{-}$are formed.
Weak base: The base when dissolved in water is ionised or dissociated partially or incompletely is known as weak base. For example, ammonium hydroxide $\left( NH _4 OH \right)$.
$\rightarrow$ In the aqueous solution of weak base, very less amount (approximately $2$ to $3 \%$ ) of solute is ionised to $OH ^{-}$. For example, In aqueous solution of $1 M ~NH _4 OH$, the concentration of $OH ^{-}$is not 1 M but it is very less than 1 M .